Latitude and longitude are spherical coordinates used to locate a point on the earth. Many maps don't need to take the curvature of the earth into account. For many applications, the earth can be assumed to be flat over a small area such as a county, so that the latitude/longitude system can be treated as a Cartesian coordinate system. Both latitude and longitude are specified in decimal degrees.
Longitude is the X coordinate and ranges from -180 degrees to +180 degrees.
Latitude is the Y coordinate and ranges from -90 degrees to +90 degrees.