What is the horizontal reference datum code?
The horizontal datum code identifies the model of the earth that supports measurements of horizontal distances. Because the earth is not a perfect sphere, mathematical models have been derived to describe the shape of the earth, the location of the center, and the location on the surface that represents the starting point for measuring coordinates. Maps and charts typically have the datum printed in the margin. The three choices for the datum are: 001 North American Datum of 1927 (NAD27): This is the model used for many USGS maps or NOAA charts. 002 North American Datum of 1983 (NAD83): This is an improved model based on earth and satellite observations which is used on many USGS and other maps. 003 World Geodetic System of 1984(WGS84): This is a newer model based on earth and satellite observations. Used on some maps and charts. Typically GPS units report location information using this datum.
