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Paper maps are historically some of the most useful documents known to
man. Indeed, here the topographic maps were to originally locate the
sinkholes and discover the tremendous depths of Sistema
Zacatón. Two
topographic maps have been scanned in a sheet scanner and opened in ARC
GIS. The Georeferencing tool is used to properly reference the maps
in real space. Steps taken include:
1. Open ArcCatalog and set the spatial reference properties of the
two map files (geotif).
This includes
setting it to UTM Zone 14 projection, NAD 27.
2. Open the geotif of one of the maps
in ArcMap, and activate the georeferencing toolbar.
3. Use the "add control point" tool
and double click on a UTM grid intersection point.
4. Use the table editing tool and
manually correct the map values to correspond with map.
5. Continue adding control points
until the RMS error drops to an acceptable level (10 m).
Once the image was
referenced well, the image was then rectified and saved. GPS points
collected in the field were overlain with topo maps to check registration
(below)
The same procedure was conducted for
the 1:250k geologic maps as well. The image below shows both the
geologic maps and the topo maps overlain in once scene.
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