A reference ellipsoid is the mathematical model of the shape of the Earth with the major axis along the equatorial radius. A geographic coordinate system uses longitude and latitude expressed in decimal degrees. For example, WGS 1984 and NAD 1983 are the most common datums today. Before 1983, NAD27 was the most common datum.
Cartographers write spherical coordinates (latitudes and longitudes) in degrees-minutes-seconds (DMS) and decimal degrees. For degrees-minutes-seconds, minutes range from 0 to 60. For example, the geographic coordinate expressed in degrees-minutes-seconds for New York City is:
- Latitude: 40 degrees, 42 minutes, 51 seconds N
- Longitude: 74 degrees, 0 minutes, 21 seconds W
You can also express geographic coordinates in decimal degrees. It’s just another way to represent that same location in a different format. For example, here is New York City in decimal degrees:
- Latitude: 40.714
- Longitude: -74.006
Latitude, Longitude and Spherical Coordinate System Grids
When you put two coordinates together as a pair (X, Y), you can locate anything on Earth.
Latitude and longitude form our coordinate system grid.
Also, you can express coordinates in different ways. For example, you can use decimal degrees or degrees-minutes-seconds.