Remote sensing data can measure the Earth in two dimensions. But we can also use remote sensing to measure the Earth in three dimensions using digital elevation data, which we include in a Digital Elevation Model. A Digital Elevation Model (DEM) is a three-dimensional representation of a planet's terrain. In the context of this book, this planet is the Earth. The history of digital elevation models is far less complicated than remotely-sensed imagery but no less significant. Before computers, representations of elevation data were limited to topographic maps created through traditional land surveys. The technology existed to create three-dimensional models from stereoscopic images or physical models from materials such as clay or wood, but these approaches were not widely used for geography.
The concept of digital elevation models came about in 1986 when the...
