Fall 2014
   GEO327G/386G: GIS & GPS Applications in Earth Sciences


 

Messages

Syllabus

Schedule

Lecture

Lab

Projects

Trip(s)


Lab 2: Map Projections and Coordinate Systems in ArcGIS v.10


Note: This exercise is a modification of material originally developed by Kristina Schneider and Dr. David R. Maidment for CE 394K: GIS in Water Resources at The University of Texas at Austin.  These materials may be used for study, research and education.  Please credit the authors.

A page of questions from this lab can be found in the Lab_2_data folder.

Part 1 - Map Projections and Coordinate Systems

Contents

2.1 Purpose

  • Gain experience in ArcMap using on-the-fly-projection of various common projections
  • Learn how to define a projection in ArcCatalog and ArcToolbox
  • Learn how to project vector data using ArcToolbox

2.2 Introduction and Summary

Recall from lecture that maps are, in essence, graphs and that creating maps with a computer is analogous to plotting points and lines on graph paper.  For software to show the geographic location of features, the features must be stored with x and y coordinates tied to a specific origin (i.e. X=0, Y=0; a "Coordinate System") and a datum.  The datum specifies the dimensions of a model of the earth; the length of the minor and major semi-axes of an ellipsoidal earth or the radius of a spheroid (see lecture notes).  Together, the datum and coordinate system comprise the so-called "Spatial Reference" of a data set.

In ESRI lingo, Spatial References are of two types:

  1. A Projected Coordinate System ("PCS"), is composed of a datum (e.g. WGS84) and coordinate system parameters (e.g. location of origin and standard parallel(s) in lat. & long., type of developable surface, false easting and northing, etc.; see lecture notes) specific to a map projectionPCS coordinates of features are stored in meters or feet relative to the PCS origin.

  2. A Geographic Coordinate System ("GCS"), includes only a datum, location of a Prime Meridian (Y-axis; the X-axis is always the equator), and an angular unit of measure.  A GCS has units of decimal degrees - GCS coordinates of features are stored in degrees of latitude and longitude.  West longitudes and South latitudes are stored as negative values and the units are decimal degrees (DD), not Degrees, Minutes and Seconds (DMS).

One of the principal, traditional strengths of GIS software is the ability to convert data stored in one Spatial Reference to another Spatial Reference.  This map projection process may involve conversion of coordinates from one GCS to another GCS, from a GSC to a PCS, or from one PCS to another PCS.  A computer screen or paper map can only have one Spatial Reference; one origin and one set of axes for the graph.  Thus, the ability to convert coordinates from one Spatial Reference to another is a key aspect if one wishes to simultaneously view data sets that have different Spatial References.

Within ArcGIS, ArcToolbox has tools to do these conversions.  In so doing, you can create a new, permanent data file containing coordinates in the new Spatial Reference. Alternatively, temporary ("on-the-fly") conversion to a different Spatial Reference is done automatically upon adding data in ArcMap.  This on-the-fly conversion permits viewing of data sets that have different Spatial References without first having to create a new file(s) of converted coordinates with an ArcToolbox tool.

For either of these processes to work the software must first know the Spatial Reference of the dataset(s).  If this information is missing from a dataset, then ArcToolbox and ArcCatalog have tools for creating it, a necessary first step (called "Defining a Spatial Reference" or "Defining a Projection") before permanent or on-the-fly conversion can be successful.  Many older data sets are missing Spatial Reference information and can produce problems if this "defining" step is ignored.  Worse still are datasets with the wrong Spatial Reference definition!  We will learn to recognize datasets with these shortcoming and to apply appropriate fixes.

2.3 Data

Files for this exercise are contained in the Lab_2_data folder, which resides in the "2014_Fall_Lab_data" folder.  To use the files, copy the entire Lab_2_data folder to your network storage space.

Some of the data are within a geodatabase, called Mapproj.mdb, that contains four feature datasets:

  • World: containing feature classes cntry94 and world30 - countries, and 30 meridians and parallels for the earth
  • USA: containing feature classes States, Counties and Latlong - states and counties of the US and a 5 grid of meridians and parallels
  • Texas: containing Quad75 and Onedegtx - a coverage of Texas showing a 1 grid and 7.5' quad map extents
  • Austin: containing Juris, Lakes, Roads - administrative boundaries of legal jurisdiction, lakes and roads in Austin, Texas.

         All of these datasets have GCS NAD83 coordinates.

Other data are contained in three shapefiles in the folder Shapefiles:

  • cenart.shp - center lines of arterial streets in the Austin area
  • polylakes.shp - lakes in the Austin area
  • creeks.shp - creeks of the Austin area

All of these shapefiles also have GCS NAD83 coordinates, but the latter two are missing Spatial Reference information.

Finally, there is a color-infrared orthophotograph of part of Austin contained in a separate folder called  Austin_E_DOQ_SW.  This is a Mr. SID format, 1-meter resolution image of the SW quarter of the Austin East 7.5' topographic quadrangle obtained from TNRIS.  The spatial reference for this file is UTM zone 14, NAD83, but, like two of the shapefiles, this information is not present in a form that can be read by the software.

  • Copy the Lab_2_data folder to your network storage space for this class.
  • Create a link to this folder in ArcCatalog (see Lab 1 if you've forgotten how).

2.41 Projections of the World

2.410 The World in Geographic Coordinates

2.411 Loading Data

  • Start ArcMap, choosing “New Maps>Blank Map” and set the default geodatabase for the project to Mapproj.mdb.  Once ArcMap opens, there will be a single Data Frame called "Layers" in the Table Of Contents (TOC).
  • Right-click on "Layers", and choose Properties. Select the General tab, and change the Data Frame name to “Geographic Coordinates”. Click OK.
  • Click the Add data button Add button, navigate to your Mapproj.mdb geodatabase and add all of the World feature dataset feature classes.
  • If necessary, drag cntry94 above world30 in the TOC.

Watch a short video of these steps.

2.412 Symbology and Labeling

You want to make the layer world30 rectangles show just their outlines, so that if needed you can show meridians and parallels on top of the countries.  You would also like to label a few of the countries.

  • Right-click on the world30 layer in the TOC and select Properties. Navigate to the Symbology tab and click on the rectangle in the Symbol cell to get the Symbol Selector window. Select the Hollow color and press OK. You should see the world in geographic coordinates.
  • To label just a few features, first right-click on the cntry94 layer in the TOC and deselect Label Features (if its on). On the Drawing toolbar (normally at the bottom of the window), there is a Label button label button that allows you to label individual features. It is found underneath the big big A button symbol in the Draw toolbar. If you don’t see the Draw toolbar, navigate to the "Customize" menu, and click on Toolbars>Draw to make it visible.
  • Click on the label button label button
  • Keep the selections chosen by the computer in the Labeling Options window. Close the Labeling Options window, and click on the countries on the map that you would like to label.

Watch a short video of these steps.

Note: when labeling this way the program assumes you want to label features in the topmost layer of the TOC.  Be sure to have the cntry94 feature class as the uppermost layer in your TOC or you will get numbers from the world30 boxes when you click on the countries to label them.

Where does the label button get the names for the countries?  To answer this question:

  • right-click on the cntry94 in the TOC, select Properties and choose the Labels tab.

The label tab contains a drop-down menu called "Label field" that contains all of the field names in the cntry94 attribute table - it has been set to NAME.  The attribute table for cntry94 contains a field called "NAME" that contains country names.

  • See this for yourself by opening and examining the attribute table for this layer.

This is where the label button looks to find the text for the labels (as do all other automatic labeling tools).  Note that from this tab you can also control the label font, its placement, the scale at which it is displayed, and select from some predefined styles.

Watch a short video of these steps.

2.413 Coordinate Display

  • Move the cursor around on the map and you will see a pair of numbers at the bottom right that change as you move the cursor. These give the location of the cursor, and from the values displayed you can see that these data are latitude and longitude displayed in decimal degrees.

If you find that the units displayed are described as “Unknown Units”, you can reset “Unknown Units” to “Degrees Minutes Seconds” (or any other units) by right-clicking the Data Frame name in the TOC, clicking the General tab, and changing the Display drop-down menu to “Degrees Minutes Seconds”. 

  • Likewise, you can change from “Degrees Minutes Seconds” to "Decimal degrees" using the same procedure.  Do So.
  • Now, SAVE YOUR MAP as World.mxd (mxd extension will be added automatically).

Watch a short video of these steps.


Questions:
1.1.1 What is the spatial extent of the view shown in degrees of latitude and longitude?
1.1.2 Where is the point (0,0) (deg. longitude, deg. latitude) located?
1.1.3 Using the Rectangle tool in the Drawing toolbar, draw a box around Australia. What is the extent of this box?  Give the coordinates of the lower left corner and upper right corner in decimal degrees.

 

 

2.411 The World in Robinson Projection

So far, we have examined the world as “unprojected” data (i.e. in geographic coordinates). Now we will view the layers cntry94 and world30 as projected data. A common projection for the world is the Robinson projection.

2.4111 Creating a new Data Frame and adding data

  • Create a new Data Frame, using Insert->Data Frame.
  • From the View menu, select Data Frame Properties. Select the General tab, and name the Data Frame Robinson.
  • Right-click on the world30 feature class in the Geographic Coordinates Data Frame, select Copy, then right-click on the Robinson data frame and select Paste Layer.  You’ll see the world30 feature class appear in the Robinson Data Frame.
  • Do the same for the cntry94 feature class. Put world30 on top of cntry94 for visual comparison of meridians and parallels.
  • Right-click on the Robinson Data Frame and select Activate to display the data in this frame.  Without this crucial last step, you will not be able to do anything with this new Data Frame.

To copy the two feature classes as a group, you could have:

  • right clicked on the original Data Frame in the table of contents (with Display tab active) and created a new "Group Layer";
  • Dragged and dropped individual layers onto the new Group Layer;
  • Copied and pasted the entire group layer to the new Data Frame.

This alternative method can be very helpful when dealing with a large number of layers.

Watch a short video of these steps.

2.4112 Setting the Coordinate System for a Data Frame

ArcMap has the ability to take data that are either in geographic coordinates or in any number of projected coordinate systems and project them to a new coordinate system within the Data Frame ("on-the-fly" projection).  To set the coordinate system of the Data Frame (in this case to the Robinson projection):

  • Right click on the new Robinson Data Frame and select Properties.
  • On the Coordinate System tab, under the Select a Coordinate System box, click the Predefined folder. Then select Projected Coordinate Systems>World>Robinson (shown below). Click OK.
  • A warning may appear, but we can ignore it for our purposes (just click Yes). Ignore this message every time it appears throughout THIS exercise (in other circumstances you may need to deal with this issue; we'll cover it in lecture).

You will see the world map appear in a Robinson projection. Pretty slick! As you can see, the landmasses appear much less distorted in this projection. It is important here to note that the files themselves have not been projected permanently—they are only displayed in the new projection. This is called “on-the-fly” projection in ArcMap, which is distinct from create new data files in different projections, sometimes referred to as "hard projection", using ArcToolbox. 

  • To better distinguish the two views of the world, change the color for cntry94 in the Robinson Data Frame

Watch a short video of these steps.

The Robinson projection is a relatively new map projection for the earth designed to present the whole earth with a minimum of distortion at any location. If you move the cursor over this space, you'll see that the coordinates are now projected coordinates (i.e. eastings and northings) reported in meters.

2.4113 Create your own Map and layout of several Data Frames

  • Create another Data Frame, and copy/paste the layers from the World Data Frame into the new data frame. Be sure to put world30 on top of cntry94 for visual comparison of meridians and parallels.
  • In the new Data Frame, play with the different projections available in the Coordinate System tab of the Data Frame Properties, and explore the different shapes the world can take.
  • Note that if you want to view a different Data Frame, right-click on the Data Frame name, and choose Activate.
  • After you’ve experimented with different projections, select one for a layout you will turn in.
  • You can create a layout that contains several different data frames. Switch to the Layout view, and you’ll see all three Data Frames displayed. By default, the Data Frames are on top of each other.
  • Resize and reposition these frames to create a more attractive map layout.
  • Be sure to add all the necessary elements to your layout (title, name, date, etc.;  a scale bar is not needed for a map of the world!). Consult the layout guidelines for help. Also, be sure it is clear which Data Frame corresponds to which projection - give each a caption or title.
  • Save the map file.
 

To be turned in: a color layout showing the world in geographic coordinates, in Robinson projection, and a projection of your choosing.  Before finalizing your layout, drag the lat-long grids below the countries to enhance map readability.  Title the layout "Map 1: Projected And Unprojected Maps Of The World".

 

 

2.42 Projections of the United States

2.421 United States in Geographic Coordinates

We will now examine map projections used for the continental United States. We could continue adding Data Frames to the previous map file, but to simplify things, let’s create a new map file.

  • Use File>New>Blank Map to create a new map file.
  • Rename the Data Frame “Geographic Coordinates” and set Display units to decimal degrees.
  • SAVE the map file as USA.mxd.
  • Add the states and latlong feature classes from the USA feature dataset of mapproj.mdb.
  • Move states below latlong in the TOC, if necessary.
  • Use the Zoom In tool and zoom to a view of just the continental US (exclude Alaska and Hawaii). Use the Pan tool to move the US into the center of the view window if necessary.

Watch a short video of these steps.

 

 

Questions:
2.1.1 What is the geographic extent of the United States? Give the eastern and western limits of longitude and the northern and southern limits of latitude of the continental US (not including Alaska or Hawaii) to the nearest degree.

2.1.2 Which parallel defines much of the border between the United States and Canada?

2.1.3 If we removed a wedge out of the earth cut along the meridians defining the most eastern and western points in the continental United States, how much of the globe would we have cut out? Give your answer as a percent of the total volume of the earth (assume the earth is a sphere for this problem).

 

 

2.422 United States in Albers Equal Area Projection

The Albers Equal Area projection has the property that the area bounded by any pair of parallels and meridians is exactly reproduced between those parallels and meridians in the projected domain. That is, the projection preserves the correct area of the earth. For example, an island with an area of 100 km2 will exhibit an area of 100 km2 in the Albers Equal Area projection. The drawback to this projection is that it distorts direction, distance and shape somewhat.

  • Create a new Data Frame and copy and paste in the layers latlong and states from the previous frame.
  • Make sure states is below latlong to enhance visual comparison of meridians and parallels.
  • Rename the data frame Albers Equal Area.
  • Bring up the Data Frame Coordinate System tab. Select the coordinate system Predefined>Projected Coordinate System>Continental>North America>USA Contiguous Albers Equal Area Conic. Zoom into the continental US.

  • Compare the United States in geographic coordinates and in the Albers projection. You should change the color of one of the layers to further distinguish them.

Watch a short video of these steps.

You will see that in geographic coordinates, the United States appears to be wider and flatter than it does in Albers Equal-Area Projection. This does not occur because Canada is sitting on the USA and squishing us! This effect occurs because as you go northward, the meridians converge toward one another while the successive parallels remain parallel to one another. When you reach the North Pole, the meridians converge at a point. In an unprojected view, the meridians are drawn as parallel lines instead of converging lines. Drawing the meridians in this manner distorts the regions between them. As you approach the poles, the meridians have to be drawn farther and farther apart in order to make them parallel. For this reason, distortion of the regions between parallels increases as you move toward the poles. A more precise geometric explanation is provided below.

If you take a 5 degree box of latitude and longitude, such as one of those shown in your ArcMap file, the ratio of the East-West distance between meridians to the North-South distance between parallels is Cos (latitude): 1.  For example, at 30N, Cos(30) = 0.866, so the ratio is 0.866 : 1, at 45N, Cos(45) = 0.707, so the ratio is 0.707 : 1. In the projected Albers Equal Area frame the result is that square boxes of latitude and longitude appear as elongated quadrilaterals with a bottom edge longer than their top edge. In geographic coordinates, the effect of the real convergence of the meridians is lost because the latitude and longitude grid form a set of perpendicular lines, which is what makes the United States seem wider and flatter in geographic coordinates.

  • SAVE the USA.mxd file.

 

 

To be turned in: A layout showing the United States in geographic coordinates and in the Albers Equal Area projection.  Before finalizing your layout, drag the lat/long grids below the countries to enhance map legibility.  Title the map "Map 2: Projected And Unprojected Maps of the Conterminous United States".

 

 

2.43 Projections of Texas

Note: A summary and commentary on common Texas projections can be downloaded here

2.431 Texas in geographic coordinates - displaying a subset

  • Create a new map document, Texas.mxd. Name the Data Frame "Geographic Coordinates".
  • Add in the feature classes counties and latlong (latlong on top) from the USA feature dataset of the mapproj.mdb geodatabase. The feature class counties contains counties of the United States, including Alaska and Hawaii. Make sure latlong is on top of counties in the table of contents.
  • To make it easier to determine the counties in Texas, right-click counties, select Properties, and go to the Symbology tab. Choose to display the counties by Categories>Unique values, and select STATE_NAME from the Value Field drop-down menu. Press the Add Values… button (don't choose Add All Values!), select Texas, and press OK (you may first have to click the button "Complete List" if Texas is not displayed in the list). Deselect the check mark for <all other values>, which will leave only counties with the STATE_NAME as Texas to be shown. Click OK.

  • Only the counties in Texas remain on the map.  Zoom in to see a larger view of Texas counties.

The latitude/longitude grid displayed is in intervals of  5-degrees. You can determine what latitude or longitude a particular line represents by moving the cursor to any line and reading the numbers displayed at the bottom right below the map view window.

  • Save your map document as Texas.mxd.

Watch a short video of these steps.

 

 

Questions:
3.1.1 What is the geographic extent of Texas to the nearest degree in North, South, East and West?
3.1.2 What meridian runs down the East side of the Texas Panhandle? (The Panhandle is the northernmost part of Texas bounded by three lines meeting at right angles.)

 

 

2.432 Texas in Lambert Conformal Conic Projection

The Lambert Conformal Conic projection is a standard projection for maps of areas whose East-West extent is large compared with their North-South extent. This projection is "conformal" in the sense that lines of latitude and longitude, which are perpendicular to one another on the earth's surface, are also perpendicular to one another in the projected domain.  Angles remain undistorted in this and all conformal projections.

  • Create a new Data Frame, copy and paste Latlong and Counties to it from the previous Data Frame. In the Properties for the new Data Frame, rename the Frame Lambert Conformal Conic, move to the Coordinate System tab and select Predefined>Projected Coordinate System>Continental>North America>USA Contiguous Lambert Conformal Conic projection.
  • Click OK.

Notice how the meridians now fan out from the north pole (a consequence of using a conic projection centered on the axis of rotation of the earth). The display shown is that produced by cutting the cone and unfolding it so that it lays flat.

  • Zoom to Texas in the Lambert Conformal Conic projection.

Watch a short video of these steps.

Notice that Texas appears to be slightly tilted to the right. This occurs because the Central Meridian of the projection is 96W, which would appear as a vertical line in the display if it were shown. Regions to the West of this meridian (most of Texas) appear tilted to the right while those to the East appear tilted to the left.

2.433 Texas in the Texas Centric Mapping System - setting a custom projection

In order to present a pleasing map of Texas, and to minimize distortion of distance in state-wide maps, the Texas State GIS Committee has approved a standard projection of Texas called the Texas Centric Mapping System. There are two variations on this projection, one is a Lambert Conformal Conic projection, the other is an Albers Equal Area. We'll use the Albers Equal Area Conic. The definition of this projection is: 

Datum: North American Datum of 1983 (NAD83)
Ellipsoid: Geodetic Reference System of 1980 (GRS80)
Map units: meters
Central Meridian: 100W (-100.0000)
Latitude of Origin: 31 15' N (31.25; we will use 18.0 for the exercise below)
Standard Parallel 1: 27 30 N (27.5000)
Standard Parallel 2: 35 N (35.0000)
False Easting: 1,500,000
False Northing: 6,000,000 

This means that the standard parallels (where the cone penetrates earth's surface) are located at about 1/6 of the distance from the top and bottom of the state, respectively, and that the origin of the coordinate system (at the intersection of the central meridian and the reference latitude) is south of Texas in the Gulf of Mexico, to which the coordinates (x, y) = (1500000, 6000000) meters is assigned so that the coordinates of all locations in the state will be positive.

  • Create a new Data Frame, and copy/paste Latlong and Counties to it from either of the previous Data Frames.
  • Double-click on the Data Frame name, select the General Tab and rename the Data Frame "Texas Centric 35.0".
  • Click on the Coordinate System tab.
  • With the "Custom" folder highlighted click the "New…" button on the right to create a new Projected Coordinate System. Fill out the parameters with the values given above and shown in the picture below.  Note that the Latitude of Origin parameter should be 18, and that no commas appear in the False Easting and Northings.
  • You also have to select a Geographic Coordinate System to specify the datum. Select North American>North American Datum 1983.

  • Click both OKs in the two dialog box and you'll see the map of Texas transformed to a nice upright appearance, the Texas Centric Mapping System. Zoom in to Texas.
  • Save your work.

Watch a short video of these steps.

2.434 Texas in Universal Transverse Mercator (UTM) Projection

The Universal Transverse Mercator projection is actually a family of projections, each having in common the fact that they are Transverse Mercator projections produced by wrapping a horizontal cylinder around the earth. The term transverse arises from the axis of the cylinder being perpendicular or transverse to earth's rotation axis. In the Universal Transverse Mercator coordinate system, the earth is divided into 60 zones, each 6 of longitude in width, and the Transverse Mercator projection is applied to each zone.

  • As before, create a new Data Frame and copy/paste Latlong and Counties to it from any of the previous Frames.
  • Double-click on the new Data Frame, and follow previous steps to rename it UTM Zone 14N. Click on the Coordinate System tab and select Predefined>Projected Coordinate System>Utm>NAD 1983>NAD 1983 UTM Zone 14N projection.

The parameters in the "Current coordinate system" box mean that the Central Meridian of Zone 14 is at 99W so that it covers from 96W to 102W; the Reference Latitude is 0.0000 (the equator, which is 0N); the origin of the coordinate system is at the intersection of the Central Meridian with the Reference Latitude and thus is at (0N, 99W), where the coordinates are (x, y) = (500000, 0) m. The False easting of 500,000m ensures that all points in the zone have positive x coordinates. The y-coordinates are always positive in the northern hemisphere because 0 is at the equator. In the southern hemisphere, a false northing of 10,000,000m is applied to the equator to ensure that the y-coordinate is always positive.

The Scale Factor of 0.9996 means that along the Central Meridian, the scale of the map is slightly reduced (distorted).  True (undistorted) scale is only achieved at two lines of secancy, which are 1.5 degrees to either side of the central meridian (see lecture notes).  The scale factor 0.9996 describes the maximum distortion within the zone; scale distortion away from the central meridian is less than this (more closely approximating a scale factor of 1, which exists only along lines 1.5 degrees away from the central meridian).

  • Click OK to see the projection applied. The pattern of meridians and parallels looks very different from those of the other projections we’ve looked at. Note how the meridians converge at both the North and South Poles.

  • Zoom in on Texas. The map of the state looks much as it did in the Texas State Mapping System using the Lambert Conformal Conic projection.

  • SAVE the Texas.mxd map document.

Watch a short video of these steps.

 

 

Questions: 
3.4.1  How many UTM zones are there in Texas?  Note that the meridians in the graphic above are not UTM zone boundaries.  You may wish to consult your notes.
3.4.2 Which zone covers West Texas? Central Texas? East Texas?
3.4.3 In the lab procedure, you referenced the UTM coordinates for Texas to Zone 14.  Why was this zone chosen instead of the others?
3.4.4. Recall that UTM zones use a false easting for the central meridian to avoid negative numbers. Place the cursor over the westernmost tip of Texas in the UTM Zone 14N data frame, and read the coordinates from the lower right part of the window. Why is the first number negative?

  • To be turned in: A color layout showing Texas in Geographic, Lambert Conformal Conic, Texas Centric and UTM projections. Before finalizing your layout, drag the latlong grids below the countries to enhance map legibility.  Be sure to save your map document after you complete the layout.  Title the layout "Map 3: Projected And Unprojected Maps Of Texas".
 
 

2.44 Projections of Austin

2.441 Austin in Geographic Coordinates - Zoom to Layer, Select by Location, Export to Shapefile

You have viewed the effect of different projections on different scales. from the world to country and state levels. In the next few steps, you will take a look at the City of Austin and the effect of two map projections upon a map of the city.

  • Create a new map document, Austin.mxd, and add in the layers Juris, Lakes, Roads from the Austin feature dataset, and Quad75, and onedegtx from the Texas feature dataset in the Mapproj.mdb geodatabase.

The feature class Juris is a coverage of the legal jurisdictions of the City of Austin. The classes Lakes and Roads show the lakes and main roads of the Austin area respectively. The feature class Quad75 is a mesh of 7.5 minute quadrangles for Texas with map sheet names for each quad, and onedegtx is a line file of a 1 x 1 degree grid of meridians and parallels. All of these data are stored in geographic coordinates relative to the NAD83 datum.

  • Double-click on the Data Frame name and rename it Geographic Coordinates.
  • Right-Click on the Juris layer and select Zoom to Layer.
  • Rearrange the layers in the TOC in the following descending order: onedegtx, Quad75, Lakes, Roads, Juris. Make the symbol for Quad75 hollow (See instructions in Step 1). Symbolize onedegtx using the Highway symbol (Red, size 3). Use a shade of blue for Lakes.

Watch a short video of these steps.

  • You can get a better picture of Austin by using the Symbology tab for the Roads layer to classify the roads by size (Size = 1 is the largest road for IH-35 and the Mopac expressway), and on the Juris layer by Name. The names correspond to surrounding cities and 2 mile and 5 mile buffer zones around the Austin city limits, called Extra Territorial Jurisdictions, or ETJ's.
  • Right-click on the Roads layer and select Properties, navigate to Symbology. Select to represent the layer with a Unique value with SIZE in the Value Field. Use an appropriate color scheme.
  • To make the roads thicker, double-click on the "All other values" line, to bring up the Symbol Selector window. Set the Width to 2.00, and then re-click on the Add All Values button in the Layer Properties window to resize all of the lines to size 2.  Make sure the all other values box is NOT checked.

  • Click OK
  • Repeat this process with the Juris layer, placing Name in the Value field. Change the Color Schemes to Pastels.

Watch a short video of these steps.

  • Click OK. You will see the City of Austin classified by legal jurisdiction.

  • The Quad75 layer shows 7.5 minute quadrangle map outlines within Texas. Right-click on Quad75 and select Zoom to Layer so that you see all of Texas displayed in 7.5 min quadrangle sheets.
  • Resize the Onedegtx lines to size 1 so that they are not too dominant in the map.  Return to your previous extent by clicking the blue, left-pointing arrow on the Tools toolbar.

At this point, we would like to produce a new file that contains a subset of the 7.5 quad outlines and names for quad maps that cover the Austin area.  So far, in order to focus on particular features in a layer, we have simply hidden them from display by not including them when we've symbolized.  We would like instead to now extract these quads from the Quad75 layer and save them as a new file.  The steps are to first select (highlight) the ones we want, then "export" them to a new file, a shapefile in this case. To select the 7.5 minute map sheets that encompass Austin, you will use one of the many selection tools available in ArcMap. 

  • From the Selection menu at the top of the ArcMap window choose Selection>Select by Location and fill in the resulting window as below. This will select features from Quad75 that intersect (see the Preview graphic at the bottom of the dialog box that shows polygons that intersect polygons) Juris.
    • Select feature from Quad75 that intersect Juris.

Select by Location GUI

You'll see a subset of the quadrangles selected on the map after you click Apply, as shown below (but not labeled).

To export the selection to a new file:

  • Right click on Quad75 in the TOC, and select Data>Export Data... ; ensure that "Selected Features" appears in the "Export:" drop-down menu and that the "Save as type:" reads "shapefile".
  • Name the resulting file AustinMaps.shp, Browse to the location where you want to save it (Lab_2_data folder on your y: drive, perhaps in a new folder), then click OK and answer yes to add it to the display.  Go to Selection>Clear Selected Features to deselect the quads you previously selected or simply use the clear selection tool Clear selection tool icon on the Tools toolbar.
  • Delete Quad75 from the TOC.
  • Right click on the new AustinMaps layer in the TOC and select Label features to show the map names. You can open the attribute table of this file, called AustinMaps.dbf, in Excel and copy the list of map names to paste into a Word document.  If you do so, be careful not to overwrite the original dbf file.
  • SAVE your Austin.mxd file.

Watch a short video of these steps.

 

 

Questions:
4.1.1 How many 7.5' quadrangle sheets are there in a 1 degree by 1 degree box?
4.1.2 How many 7.5' quadrangle sheets are needed to cover Austin?  Hint: Open the Attribute table for the AustinMaps layer and examine the bottom of the window.  The number of records (there is one record for each quad) in this file is given.
4.1.3 Just Southwest of Austin there is an intersection of a 1 parallel and a 1 meridian. What is the latitude and longitude of this location?
4.1.4 By opening the AustinMaps.dbf in Excel, make a list of the names of the 1:24,000 scale map sheets (7.5' quads) that are needed to cover Austin.  Cut and paste this list into your answer sheet.

 
 

2.442 Austin in State Plane-1927 Projection - Layer Files

The Texas State Plane - 1927 projection is really a family of projections for Texas, which has five State Plane zones (see lecture notes).  Each zone is projected using the Lambert Conformal Conic projection, with different projection parameters depending on the zone.  Austin is in the Texas Central Zone. 1927 refers to the North American Datum (NAD) 27 datum.  Unlike 1983 Texas State Plane projections, 1927 State Plane units are survey feet (see class notes).

  • Create a new Data Frame; name it State Plane – 1927. Add Juris, Lake, Road, Quad75, and onedegtx from the geodatabase, as in the previous Frame.  This is easiest by selecting all of the dataset in the TOC (hold the Ctrl key down as you click on the layer names), right-click "Copy", click the new Data Frame, and right-click "Paste layer(s)".
  • Click the Coordinate System tab in the frame's Properties window and select Predefined>Projected Coordinate System>State Plane>NAD 1927>NAD 1927 Stateplane Texas Central FIPS 4203 projection. Click OK.
  • Right-click on Juris and select "Zoom to Layer". Play with the Symbology until it looks similar to that in the Geographic Coordinates Frame. (It may already look identical - v. 10 seems to have added this feature.  Assume for the sake of the discussion below that the symbology of the Juris layer in each Data Frame is different).

Watch a short video of these steps.

There are, in fact, two  better way to make the Juris layer symbology match that of the earlier Data Frame.  You could either copy and paste the Juris layer in from the the previous Data Frame or, to preserve this symbology for future use, you could create a "Layer File".  A Layer file contains no actual spatial data, only a description of a layer's symbology.  Once created, it can be applied to the same spatial data in other data frames or in other map documents.  This can be very useful when sharing previously symbolized data with others. Symbology is only preserved within a map document and is otherwise not attached to a data file unless it is saved separately as a layer file.  Without a layer file, a complicated color scheme for a geologic map with many colors and patterns representing rocks types, for example, would have to be recreated each time the file was added to a map document.  Thinking back to Lab 1, the reason you could see the colors and patterns I had created for the geologic map of Texas was because the map unit polygon file was accompanied by a layer file.

To create a layer file:

  • Activate the Geographic Coordinates Data Frame (right click, Activate)
  • Highlight the Juris layer in the TOC
  • Right-click on the Juris title in the TOC, choose "Save as Layer file...", and save the layer with the default name to a location on your y: drive.

To apply a layer file's symbology:

  • Activate the State Plane Data 1927 Data Frame
  • Bring up the Symbology tab for the juris layer Properties, click the Import button in the upper right, select "import symbology definition from another layer in the map or from a layer file" and browse to your saved layer file before clicking OK.

Watch a short video of these steps.

 

 

To be turned in: A Layout showing Austin in geographic coordinates and in State Plane coordinates. Before finalizing your layout, drag the latlong grid below the countries to improve map legibility.  Title you map "Map 4: Projected And Unprojected Maps Of Austin, Texas".

 
 

2.45 Projection in ArcToolbox

2.451 Project Wizard

Up until now we have changed the projection of the Data Frame ("on-the-fly projection") but not the actual projections of the feature classes.  Within the ArcToolbox module, ArcGIS offers a set of tools to project data files and save them as a new file in a new coordinate system.  There are also a set of tools for assigning projection information to data that are already projected, but for which such information is lacking.  This latter process is referred to as defining a projection or defining a spatial reference, and should not be confused with the process of actually producing and saving new coordinates for a data file through projection.  We begin first with the projection tool,  "Project Wizard", to project a feature class.

Before we do, a simple question:  If on-the-fly projection works so well, why bother projecting data to new coordinate systems?  Two reasons: 1) On-the-fly projections is not as rigorously as actual "hard" projection of data to new coordinates, so that for exacting work slight mismatches that result from on-the-fly projection of data in different coordinate systems are often unacceptable; 2) Certain geoprocessing tools that compare different data layers only work if the layers are in the same coordinate system - one or more layers might have to be converted to a different projection to use the tool.

  • If you have not already done so, SAVE your map document, always a good practice before using any tools in ArcToolbox.
  • Open ArcToolbox from within ArcMap.  New in version 10, you do not need to close ArcMap before using ArcToolbox tools on files that are open in an ArcMap document if you activate ArcToolbox from within ArcMap.  The same is not true, however, if ArcToolbox is opened from outside of ArcMap, or sometimes if ArcCatalog is open within ArcMap.  Remember, If a toolbox operation fails, the first thing you should try is to close ArcCatalog and ArcMap and try again with stand-alone ArcToolbox.
  • Open ArcCatalog from within ArcMap.
  • In ArcToolbox, navigate to "Projections and Transformations", located in Data Management Tools. The picture below shows the tools available for projection in ArcGIS 10.0/ArcInfo (some of these tools may not be available with an ArcView or ArcEditor license) that permit projection and projection definition of "Features" and "Rasters" (more on these data types later in class).

Data Management Tools - Projections and Transformations

 We are going to project the entire contents of the Austin feature dataset from Geographic coordinates to State Plane coordinates.

  • Expand the "Feature" toolbox by clicking on the + sign next to it, then double click on "Project" tool.
  • Click on the browse folder button in the "Input Dataset or Feature Class" form field, and navigate to the Austin feature dataset (notice that we are projecting all of the feature classes within the dataset in one operation) in the Mapproj.mdb geodatabase on your Y: drive. The "Input Dataset..." and "Output Dataset..." fields should now appear similar to that shown in the picture below.

Projection GUI

  • Press the Select Coordinate System button , press the Select… button. This button will allow you to select a predefined coordinate system. Navigate through to: Projected Coordinate System>State Plane>NAD 1983 (feet)>NAD State Plane Texas Central FIPS 4203 (Feet) and click Add, then click Apply.
  • Press OK. The window now displays the Output Coordinate System.
  • The optional "Geographic Transformation" field allows us to convert the data to another datum.  Because our new files will use the same datum (NAD83) as the old files, we do not need to enter anything here.
  • Press OK.   The new feature classes are created in a new Feature Dataset called Austin_Project and automatically added to the active Data Frame in ArcMap.
  • Delete these new files from the ArcMap TOC; they are simply a copy of what you already have, but in a different coordinate system.  They don't look offset from the other data because they are being projected on-the-fly to the Coordinate system of the active Data Frame.

Watch a short video of these steps.

With just a few clicks, you've projected all of the feature classes in the Austin feature dataset to State Plane coordinates!! This process would have taken many more steps and a lot more time in earlier GIS software. You have the power! And you’re not afraid to wield it!!

  • Within the ArcCatalog tree, browse to the Maproj.mdb geodatabase and you'll see that you've got a new feature dataset with copies of the three feature classes in the Austin feature dataset with a "_1" added to the name of each:

  • Open a new ArcMap document.
  • Add the contents of the Austin_Project feature dataset.
  • Open the Properties of the Data Frame and change the name to Projected. Then go to the Coordinate System tab and notice the projection is NAD_83_StatePlane_Texas_Central_FIPS_4203 (feet), as required. Pretty cool!!

  • Notice the numbers in the lower right hand corner are not latitude and longitude any more. They are in Texas central zone State Plane coordinates of feet.
  • Right click Juris, and select Open Attribute Table. Navigate to the right-hand end of the table. You’ll see that two new fields have been created, Shape_Length and Shape_Area, which refer to the length (ft) of the perimeter and the area (ft2) of the polygon, for each feature in the Juris layer.

Watch a short video of these steps.

If you want, you can project the 7.5 quadrangle map and the 1 degree grid similarly and add them to the new data frame. Verify that it looks the same as the Austin in State Plane data frame in your earlier map file.

 

 

Question
5.1.1 The area where the City of Austin has "Full Purpose" jurisdiction is the area in the center of this map. The areas around it are areas is where the City has limited jurisdiction, or that are within surrounding cities. Over what percent of the area shown in the Juris polygons does the City of Austin have "Full Purpose" jurisdiction?  Briefly explain how you got the answer, and show any calculations you use.

 

 

2.46 Defining a Spatial Reference

To project data on-the-fly or with a "Project" tool, ArcMap must know the coordinate system (also called the Spatial Reference) of the data.  Depending on the data type (e.g. shapefile, feature class, coverage, images; more on this later), this spatial reference information is either stored internally (geodatabase, coverage, some rasters) or within a separate file.   When spatial reference information is lacking,  ArcMap cannot successfully project data with different coordinate systems.  This is a common problem for lots of GIS data, such as shapefiles created with, or for older versions of, ArcView, many aerial photographs, and maps you might yourself scan for use in a GIS.  

Tools are available in ArcToolbox to create spatial reference information files.  Spatial references can also be defined in ArcCatalog.   ArcToolbox contains a "Define Projection" tool for this procedure; in ArcCatalog we can define or alter a file's XY Coordinate System.  Both techniques are examined below.

2.461 Defining a spatial reference for an aerial photograph or image in ArcCatalog

  • Open a new map document in ArcMap.
  • Add the cenart.shp shapefile from the Shapefiles folder.  This file shows major Austin streets.  As before, the Data Frame adopts the coordinate system of the first file added, in this case, decimal degrees relative to NAD83 (verify this by examining the Data Frame Properties).
  • Click the Add data button and browse to the Austin_E_DOQ_SW folder of the Lab_2_data folder in your y: drive and add 3097433a.sid, a digital orthophoto of the SW quarter of the Austin East quadrangle (which includes the UT campus).  Note that this photo is composed of three bands; to add all of them at once DO NOT double-click on the name, rather, click once and then click the Add button in the dialog box.
  • Where is the photo?  Even though it was added, it's not visible in ArcMap.  To view it, right-click on the photo name in the TOC and "Zoom to Layer".  Where did the streets go?
  • Note the coordinates in the lower right corner of the map view window when the cursor moves over the photo - they are in the range of 100's of thousands and millions of decimal degrees!  Clearly nonsensical.  What's going on?
  • Hit the full extent tool on the Tools toolbar.  The map view again goes white - nothing is visible.  The "full extent" of this map covers hundreds of thousands of degrees in East-West extent and over a million degrees in North-South extent.   The R.F. scale on the menu bar at the top of the window now reads in the trillions! - the layers are so small at this scale that they are literally invisible!
  • The problem is that ArcMap has interpreted the coordinates of the photo as decimal degrees.  It has done so because the photo does not have a spatial reference file, and the Data Frame coordinates are decimal degrees.  You were warned of this by a message box, seen below, when the photo was added.  Without spatial referencing information, ArcMap will always assume that the data are in the same coordinate system as the Data Frame, in this case GCS NAD83.

  • Close ArcMap, do not save this map document.

Watch a short video of these steps.

  • Within Arc Catalog, browse to the 3097433a.sid file and click the metadata tab in the right half of the window.
  • Click the Spatial tab in the metadata window of ArcCatalog.  The Spatial metadata indicate that the projected coordinate system for these data is NAD_1983_UTM_Zone_14N.  UTM data have coordinates in meters.  ArcMap treated them as if they were in decimal degrees, thus the problem.
  • Right-click on the 3097433a.sid file name in the Catalog tree, choose Properties and bring up the Raster Dataset Properties dialog box and scroll down the box to the see the view shown below:

As shown above, the Spatial Reference for this file is <Undefined> - ArcMap thus had to assume a default, which it chose as the coordinates of the Data Frame.  It's meters, not decimal degrees, so it chose wrong.  To fix the problem we need to explicitly Define the spatial reference.

To define the spatial reference:

  • In the Raster Dataset Properties dialog box, Click the Edit... button, then Select.., then navigate to Projected Coordinate System>Utm>NAD 1983>NAD 1983 UTM Zone 14N.prj and click Add and OK twice.
  • To check your result, examine the dialog box.  The spatial reference for the photo is now defined, as shown below.

  • Open a new map document in ArcMap, add the cenart.shp shapefile first and then add the 3097433a.sid photo.  Because you added cenart.shp first, the Data Frame has an unprojected, decimal degree coordinate system (the coordinate system of first file added, remember?).

  • Zoom to the area of the UT campus and note the close correspondence of the cenart layer with the roads on the photo, like in the area near the Erwin Center, below.

ArcMap has placed the photo, which is stored in UTM coordinates of meters, on-the-fly, into the decimal degree coordinate system of the Data Frame!  Amazing!

  • Leave this map document open in ArcMap and continue reading.

Watch a short video of these steps.

2.462 Defining a spatial reference for a shapefile in ArcCatalog

  • Within ArcCatalog, browse to your Lab_2_data Shapefiles folder.  Open the folder, right-click the polylakes.shp file (as the icon and file name indicate, this is a polygon shapefile of Austin area lakes) and select Properties... to bring up the dialog box shown below.

  • As discussed in last week's lab, this box shows the detailed properties of this file.  If not already on top, click the "XY Coordinate System" tab.

  • This tab gives Spatial Reference of the file.  As shown below, the Spatial Reference is "unknown", meaning there is no file associated with this data set that gives the Coordinate System the data are stored in.  As noted above, this is a common problem for older data sets, particularly shapefiles, that were created before ArcGIS was introduced in 2001.  If metadata are available this can be corrected.

  • To define the spatial reference in ArcCatalog:

  • Click Select>Geographic Coordinate Systems>North America>North American Datum 1983.prj, then Add, then OK. 

Through these steps you have created a .prj file, a file that was originally lacking for this dataset.  The file has the same name as the shapefile, but with a .prj extension, and is stored in the same location.  ArcMap now has what it needs to properly project this file on-the-fly. 

  • Drag and drop the polylake.shp file from the ArcCatalog tree into the ArcMap map view.

  • Change the lake symbology to hollow with blue edges so you can see the photo beneath (drag the lake layer above the photo in the TOC if it's not already there).

  • Compare the lake outlines of the photo and shapefile.  They should coincide.

  • SAVE the map document but do not close ArcMap.

Watch a short video of these steps.

 

 

Question:
6.2.1 Give two plausible reasons why the shores of Town Lake on the photo do not exactly coincide with the Town Lake outline of the shapefile.

 

 

2.463 Defining a spatial reference for a shapefile in ArcToolbox

A Spatial Reference can also be defined in ArcToolbox.  You might use ArcToolbox for this procedure instead of ArcCatalog if you had a lot of files to define.  ArcToolbox will allow you to do this in "Batch" mode, permitting definition of a spatial reference for many files in a single pass.  We will do it for just a single file, which could be done just as easily within ArcCatalog using the procedure you just completed.

  • The shapefile creeks.shp in the Lab_2_data>Shapefile folder shows creeks in Travis county.  It also lacks a prj file and thus its coordinate system is "unknown" by the software.  Using the above procedure verify this in ArcCatalog, but DO NOT correct it in ArcCatalog.

  • Open ArcToolbox and find the "Define Projection" tool by navigating the path: Data Management Tools>Projections and Transformations.  It's at the bottom of the "Projections and Transformation" toolbox.

  • Open the Define Projection tool, click the yellow folder button, browse to your copy of creeks.shp and double-click on the file name to complete the first step of the wizard, yielding a dialog box similar to that below (the path to the file will be different).

  • Press the Select Coordinate System button , then press the Select… button. This button will allow you to select a predefined coordinate system.

  • Navigate through to: Geographic Coordinate System>North America>North American Datum 1983.prj, then click "Add", "OK", and "OK".

As with the similar procedure in ArcCatalog, these steps make a .prj file that ArcMap can use to properly align data during on-the-fly projection.

  • Add the  creeks.shp file to the ArcMap document you still have open.  You should now have a map that, when magnified and symbolized, resembles the one below.

Watch a short video of these steps.

 

 

Question:
6.3.1 You have downloaded digital orthophotographs and several shapefiles from the web.  List the general steps (not the detailed procedures) that you will do to assure that the data will display properly (i.e. with the proper coordinates) in ArcMap.

 

 

You're Done!

 


Last updated
August 24, 2014
Comments and questions to helper@mail.utexas.edu
Geological Science,  U. Texas at Austin