7.4 The 30-Arc Seconds Elevation Model GTOPO30

The 30 arc second (approximately 1 km) global digital elevation data set GTOPO30 only contains elevation data, not bathymetry. The data set has been developed by the Earth Resources Observation System Data Center and is available from the web page

http://www.edcdaac.usgs.gov/gtopo30/gtopo30.html

The model uses a variety of international data sources. However, it is based on raster data from the Digital Terrain Elevation Model (DTEM) and vector data from the Digital Chart of the World (DCW). The GTOPO30 data set has been divided into 33 pieces or tiles. The tile names refer to the longitude and latitude of the upper-left (northwest) corner of the tile. The tile name e020n40 refers to the upper-left corner of the tile. In our example, the coordinates of the upper-left corner are 20 degrees eastern longitude and 40 degrees northern latitude. As example, we select and download the tile e020n40 provided as a 24.9 MB compressed tar file. After decompressing the tar file, we obtain eight files containing the raw data and header files in various formats. Moreover, the file provides a GIF image of a shaded relief display of the data.

Importing the GTOPO30 data into the workspace is simple. The Mapping Toolbox provides an import routine gtopo30 that reads the data and stores it onto a regular data grid. We import only a subset of the original matrix:

     latlim = [-5 5]; lonlim = [30 40]; ...