This lesson has introduced several important spatial referencing concepts.
Cartesian and polar coordinate systems, which are based on orthogonal
axes, were discussed, as well as the most widely used spherical system
based on latitude and longitude. We have also covered the concepts related
to the shape of the Earth, including geodetic datums, geometric Earth
models, reference ellipsoids and Earth surfaces. It is important to be
aware of the fact that a variety of reference systems is in use to describe
locations on the Earth.
"Whether you treat the earth as a sphere or a spheroid, you must transform
its three-dimensional surface to create a flat map sheet. This mathematical
transformation is commonly referred to as a map projection. One easy way
to understand how map projections alter spatial properties is to visualize
shining a light through the earth onto a surface, called the projection
surface" (ESRI, 2003). In this lesson we have had a detailed look at different
types of map projections. We have discussed cylindrical, azimuthal, and
conic projections. The concepts of tangent vs. secant projections have
been explained as well as conformal and equal area projection properties.
You should now be able to recognize and distinguish the characteristics
of the main types of map projections.
This lesson concentrated on the problem of map projections having different
sets of projection parameters. Each set is related to a particular projection
and it is very important to have a sound understanding of this relationship
between map projections and their specific parameters. In the second part
of this lesson we had a detailed look on the Universal Transverse Mercator
system as an example of a grid system that is widely used in GIS operations.