I wanted to put together a quick and dirty map of a biological reserve in Ecuador, sort of a laptop exploration of a place quite distant. At first, I thought I’d use Shuttle Radar Topography Misssion data to get the elevation information. Then I discovered the ASTER Global DEM which is 30m resolution for the whole world. Wow. Cool cool data. (I used the Japanese site to download, as I had trouble getting the US site to load).
So, first I downloaded and extracted the zipped geotiffs that come from the ASTER Global DEM. I extracted the DEMs into the same directory, and mosaicked them into a single DEM:
gdalwarp AST*.tif ecuador_aster_dem.tif
Then I created a hillshade version of the DEM for mapping:
gdaldem hillshade ecuador_aster_dem.tif ecuador_aster_hillshade.tif
and then 100 and 50 meter contours for the site:
gdal_contour -a elev -3d -i 100 ecuador_aster_dem.tif ecuador_aster_contour_100.shp gdal_contour -a elev -3d -i 50 ecuador_aster_dem.tif ecuador_aster_contour_50.shp
I loaded it all into Quantum GIS, symbolized it, and added some OpenStreetMap data. To do this, I navigated to the location in OSM, chose the download tab, and chose OpenStreetMap XML Data as my output. Using the OSM plug-in in QGIS, I imported the file, and walla– a nearly functional map.