Topographic Maps Lab

Last Modified: 08/20/09

Topographic maps not only display the locations of rivers, streets, buildings, etc. as planimetric maps (such as road maps) do, but also show the topography (land elevation and shape).

Overheads shown in class

Click on the topic below to jump to that section:

• Map Grids (Longitude and Latitude)
• Contour Lines
• Map Scales
• Gradient
• Vertical Exaggeration

Map Grids:

Latitude: Rings around Earth parallel to equator

Divided into 90°S and 90°N around the equator (0°)

Longitude: Circles that pass through both poles (MERIDIANS)

Divided into 180°E and 180°W around the Prime Meridian. The Prime Meridian passes through Grenwich, England.

Ex.) Latitude: 37°14'32"N Longitude: 97°32'15"E

Conversions:

1 degree(°) = 60 minutes(') = 3600 seconds(")

* Up to Topographic Topic List *

Contour Lines:

Contour Line: Connects all points of equal elevation on the land surface.

Contour Interval: The difference in elevation between adjacent contour lines.

Relief: The difference in elevation between local high and low spots.

Important Rules obeyed by Contour Lines:

1. Contour lines never run into a body of water
2. Contour lines never cross one another
3. ALL contour lines are closed loops
4. Contour lines point, or "V" upstream

Additional things to know about Contour Lines:

• If contour lines are closely spaced it represents a steep slope.
• Conversely, if contour lines are widely spaced it represents a gentle slope.
• Review methods on how to contour a map and know the symbol for a depression.

* Up to Topographic Topic List *

Types of Map Scales:

Ratio Scale: ratio where 1 unit on the map equals X units on the ground

Ex) 1:24000 (1 inch on map = 24000 inches in the real world)

Note that the units are the same (a ratio of inches to inches or feet to feet...).

Verbal Scale: 1 inch = 2000 feet

Bar Scale: a map "ruler"; graphical scale (example below)

Note that unlike the other map scales, the bar scale will always remain accurate for a map even when the map is reduced or enlarged.

* Up to Topographic Topic List *

Gradient

The gradient tells you the slope of the land between two points. It is calculated by dividing the relief by the path distance. Path distance is the distance measured along the path travelled (NOT necessarily the straight line distance!).

For example, if you were planning a canoe trip, you may want to know the gradient between your starting point upstream and your stopping point downstream. If your starting elevation was 50 feet above sea level, and your ending elevation was 20 feet above sea level, the relief would be (50-20) or 30 feet. Although the straight line distance between your starting and ending points may only be 2 miles, with the curvature of the river the actual path distance is greater--let's say 3 miles. The gradient therefore = 30 feet / 3 miles = 10 feet per mile!

* Up to Topographic Topic List *

Vertical Exaggeration

Vertical Exaggeration: gives the number of times the vertical scale is exaggerated relative to the horizontal scale.

Ex.) Horizontal Scale: 1 inch = 2000 feet, Vertical Scale: 1 inch = 500 feet

VERTICAL EXAGGERATION = (1/500)/(1/2000)= 4 times

Note that you get the horizontal scale from the map scale. You determine the vertical scale from the topographic profile by measuring how much relief is represented by one inch on the topographic profile.

* Up to Topographic Topic List *

Back to Cory's Geology 303 Lab Home Page