Smathermather's Weblog

Remote Sensing, GIS, Ecology, and Oddball Techniques

Mapping places unknown– free global datasets and FOSS GIS are a great combo

Posted by smathermather on January 31, 2010

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.

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