Working
with map projections
A map projection
is used to convert data from a geographic coordinate system to a projected
(planar) coordinate system. Just like there are many geographic coordinate
systems, there are many different map projections as well —each preserves the
spatial properties of data (shape, area, distance, and direction) differently.
Maps are
always flat, so do you always need a map projection? The answer is maybe—it
depends on what you want to do.
For
example, suppose your project doesn't require a high level of locational
accuracy—you won't be performing analysis based on location and distance or you
just want to make a quick map. In these situations, there is probably no need
to convert your data to a projected coordinate system.
However,
if you need to perform analysis (measure distances, calculate areas and
perimeters, determine the shortest route between two points) or if you need to
show a particular spatial property for features on a map as it really exists on
the earth, you should use a map projection to convert your data to a projected
coordinate system.