Geographic Coordinate
A geographic coordinate system uses a threedimensional
spherical surface to define locations
on the earth. Horizontal lines, or east-west lines,
are lines of equal latitude, or parallels. Vertical
lines, or north-south lines, are lines of equal
longitude, or meridians. These lines encompass
the globe and form a gridded network called a
graticule.
Longitude and latitude are angles measured from the
earth's center to a point on the earth's surface.
The angles often are measured in Degrees,
Minutes, and Seconds where 1 Degree=60
nautical miles (69.09 miles); 1 Minute=1
nautical mile; and 1 Second=100.8 feet.