DEM (Digital Elevation Model)



http://www.soest.hawaii.edu/coasts/data/oahu/dem.html

This is a DEM (digital elevation model) of Oahu, Hawaii.  According to the USGS, "A digital elevation model (DEM) is a digital file consisting of terrain elevations for ground positions at regularly spaced horizontal intervals."  This image was taken from a satellite, which is remote imagery, and this image was used to show the elevation of Oahu's coastline.

DEMs produced by the USGS can be produced using five different elevation products, and depending on which elevation product that is used, and many other variables, the image can be either more accurate or less.

The link below is used to reference the information quoted by the USGS:
http://rmmcweb.cr.usgs.gov/elevation/dpi_dem.html