What resolution is the terrain data?
The hi-res terrain data has an elevation data point every 3 arc-seconds (about 300 feet) — totalling almost 1.4 billion data points for the continental U.S.. Our proprietary compression takes this data from an uncompressed size of 2.8Gb down to about 470Mb — small enough to fit on a CDROM. For non-US areas, we currently have a mix of high-res and medium-res terrain files with a data point every 3000 feet. The lo-res terrain (for backup) has the maximum terrain elevation in each 7.5-arc-minute quad in the world, and is derived from the SRTM30 elevation data.
