DEM

http://www.usgs.gov/features/lewisandclark/Mapping.html

This is an example of graphical elevation data for the St. Louis, Missouri area. Elevation data are an essential part of many Earth science applications. They are used for such diverse purposes as providing shaded-relief backgrounds, stratification in land cover classification, geometric and radiometric correction of remotely-sensed data, landform characteristics such as slope and aspect, and for geographic information system analysis of synthetic drainage networks and watershed delineations.