difference between projected and geographic coordinate system

difference between projected and geographic coordinate system

a.    Geographic Coordinate System (GSC):

1.  A global or spherical coordinate system such as latitude-longitude. These are often referred toas geographic coordinate systems.
2. A geographic coordinate system (GCS) uses a three-dimensional spherical surface to definelocations on the earth. A GCS is often incorrectly called a datum, but a datum is only one part ofa GCS. A GCS includes an angular unit of measure, a prime meridian, and a datum (based on aspheroid). The spheroid defines the size and shape of the earth model, while the datum connects thespheroid to the earth's surface.

b.    Projected Coordinate System (PCS)

1. A projected coordinate system such as universal transverse Mercator (UTM), Albers Equal Area, or
   Robinson, all of which (along with numerous other map projection models) provide various mechanisms
   to project maps of the earth's spherical surface onto a two-dimensional Cartesian coordinate plane.
   Projected coordinate systems are referred to as map projections.
2. A projected coordinate system (PCS) is defined on a flat, two-dimensional surface. Unlike a
   GCS, a PCS has constant lengths, angles, and areas across the two dimensions. A PCS is always based
   on a GCS that is based on a sphere or spheroid. In addition to the GCS, a PCS includes a map
   projection, a set of projection parameters that customize the map projection for a particular
   location, and a linear unit of measure.