The Digital Elevation Model (DEM) consists of digital data about the elevation of certain points on a planet. This means you have a set of points (usually in a quadratic grid) with the elevation above ground level. It is part of a Digital Terrain Model and Geographical Informations Systems.

The data can be used as topographic maps or to create 3D images or movies.
There are several organisations offering this information for free in the Internet. The whole earth is available with a grid of about 1 km (30 arc-seconds)between the points in several versions. Most of the USA is available for download in a higher resolution, as some other parts of the world.

There is also enough free software to create movies of flights from on point to an other or to display how earth would look with a different waterlevel ec. You can of course use the data for own programs.

Some of the data: Globe Project: 1 km grid whole earth
GTOPO 30: 1 km grid whole earth