Sources of geospatial data in raster format

One of the most enthralling aspects of programs such as Google Earth is the ability to "see" the Earth as you appear to fly above it. This is achieved by displaying satellite and aerial photographs carefully stitched together to provide the illusion that you are viewing the Earth's surface from above.

While writing your own version of Google Earth would be an almost impossible task, it is possible to obtain free satellite imagery in the form of raster-format geospatial data, which you can then use in your own geospatial applications.

Raster data is not just limited to images of the Earth's surface, however; other useful information can be found in raster format—for example, digital elevation maps (DEMs) contain the height of each point on the Earth's surface, which can then be used to calculate the elevation of any desired point. DEM data can also be used to generate two-dimensional images that represent different heights using different shades or...