How to use digital topographic maps and other GIS files
By David Doyle
Last update 03/05/2005
What can you do with the GIS Files?
With the information here and some free programs and data you can:
What do you need?
You will need the following:
How to view the topographic maps
1) Download and install a GIS viewer such as Global Mapper. This is a free program you can download from http://www.globalmapper.com/
2) Download the data.
3) Open the map in the viewer.
If you see a message like the image to the left, click “OK” and you will see: a menu like the next image. Here you will need to enter the projection information for your map. You may have to contact the site where you downloaded the DRG from. (the info here is what is needed for DRGs downloaded from http://kyvenutian1.state.ky.us/ogis/secure/sid_index.html for maps from the southern part of Ky.
You should now see the topo map. The image below and to the left is an area of the southern part of Bowling Green North map. Notice that the map is cut off at the edge of the topo. One advantage of using DRGs is you can obtain seamless topos and up load more than one at a time. The image to the right shows the same section with Bowling Green North and South opened at the same time.
|Bowling Green North only||Bowling Green North and South|
How to Obtain Latitude and Longitude
As you move the mouse around the map, the coordinates are displayed in the bottom right portion of the screen. See the image to the right.
You can change the way the coordinates are displayed by going to “Tools” and then “Configure” and then click on the “General” tab. You can select degrees / minute / seconds (37º 00’ 00”) or degrees / minute.xxx (37º 00.000”) or degrees.xxxxxx (37.000000º).
NOTE: Keep in mind coordinates need to have the datum referenced. To check the datum for the map, go to “Tools” then “Control Center” then click “Metadata” tab and then click on the “GeoTIFF Tags” tab. Look in the projection section. For example the Gaging Station shown above has a location of Latt North 37º 00’ 05” / Long West 86º 25’ 50” and the datum is NAD83.
How to measure distance and area
To measure a distance, click on the “Measure Tool” tool in the tool bar and then click on the starting point and then move the curser to the end point. The distance is displayed in the bottom right of the screen. For example the distance from the Gaging station to the bench mark is 1544 feet.
To measure the area, use the “measure tool” as above and outline the area you wish to measure. For example the area inside the circle containing the 3225 is 0.00421 square miles and the distance of the perimeter is 1218 feet.
How to Obtain Elevation information
First load the DEM of the map into Global Mapper. DEM for Bowling Green North will appear as the image below and to the left. Now go to “file” then “Load into Current” and select the DRG. Now go to “Tools” and then “Path Profile / LOS”. Now click on the starting and ending points and you will see something like the image below.
To change the units right click on the profile and change the units as below. Go to “Tools” and then “Control Center” then select the DEM then select “Options” and then set the units and then click “Apply”.