Importing Topographic Maps into NetLogo: A Study Guide

Sometimes it is important to have the topography of an area one is trying to model because it may be unique in some way.  To facilitate the desire to have a model represent some real topography, data available from the United States Geological Survey can be modified and read into a NetLogo model. The process requires the downloading of National Elevation Data (NED) from the USGS Seamless Data Distribution website. The address for this website is http://seamless.usgs.gov/.  You might try another website at: http://gisdata.usgs.net/website/Map_Studio/viewer.asp/ .

This page allows you to view and download Data sets from original Digital Elevation models stored by the USGS.  When you click on the “View and Order Data Sets-United States Viewer” he/she will be sent to the main map page that looks like the following:

The scale bar at the bottom of the window (in this figure it reads 0 to 1154 mi) is important in getting the files down to a manageable size. This page defaults to the zoom function. Click anywhere on the United States the map resizes and zooms in to a more detailed view.  To download files of manageable size, try to zoom to the point that the scale bar reads about 0-5 mi. Some files will still be very large as the map might be a 10 meter map instead of a 30 meter map. Now, zoom to a location of interest and a scale of about 5 mi.

The topographical graph will now look like the one above.  This is a good time to consider the memory capacity of the user’s machine. To manipulate the maps with any kind of facility, the user’s machine should have a minimum of 256 Megabytes of RAM memory.  Downloading the files to your hard drive will use large pieces of the hard drive when they are decompressed. This is not an exercise one does on a computer with less than a gigabyte of hard drive space and 128 megabytes of RAM memory. 

Find the part of the map of interest, click on the download selection tool at the bottom left. (since NetLogo world is rectangular, use the rectangle.)  Click and drag across the portion desired. The selection tool will draw a green box if the file is not too big.  If the selection exceeds the maximum download size, the box becomes red indicating that the file can be ordered on CD but not downloaded.  Select the portion desired and the screen changes to the following:

This page shows the user’s request showing the NED with its latitude and longitude, size, and format and the Land Cover file also with latitude and longitude and format. Modify this format to use .BIL file type. Click “Modify Data Request”.

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