As a follow-up to the Using Map Projection Routines in IDL webinar, I wanted to show an example of reading entities from an ESRI Shapefile and visualizing them in a map projection. I’ve uploaded the example program and the Shapefile used in the example to the VIS Code Library; they can be downloaded directly from here.
For data, I chose a U.S. Census Bureau 2008 TIGER/Line® Shapefile containing county boundaries for the state of Colorado. This Shapefile, and others for Colorado, can be obtained from the U.S. Census Bureau at http://www2.census.gov/cgi-bin/shapefiles/state-files?state=08.
In the example program, NG_COLORADO_COUNTIES, a user can pass the name of a Colorado county as a string. The shape for the county is extracted from the Shapefile and displayed on a map projection. For example, to display Summit County, call NG_COLORADO_COUNTIES with:
IDL> ng_colorado_counties, 'Summit', fill_color='dodger blue'
Here’s the result:
Please try the example and read over the code—I tried to explain each step of the process: reading entities from the Shapefile, setting up a map projection and visualizing the entities in the map projection. If you have any questions, please let me know in the comments!
Hello there,
Your code is really interesting for me but for some reason IDL cries on this line:
map = map(‘Orthographic’, limit=[minlat, minlon, maxlat, maxlon], $
center_longitude=0.5*(minlon+maxlon), title=county_names[i_county] + ‘ County, Colorado’, $ color=’gray’, label_position=0)
% Unable to concatenate variables because the dimensions do not agree: .