1.2. Projections, Coordinate Systems, and Datum

Mapping the Earth requires a mathematical projection that enables us to view a spherical body on a two-dimensional surface. The problem of representing a sphere on a 2-D surface is that in almost all cases at least some part of the map becomes distorted due to the curvature of the Earth. To account for this problem, we have created Geographic Coordinate Systems (GCS) and datums to better represent our objects of study. Geographic Coordinate Systems contain X, Y, and Z data that provide standardized locations of objects on Earth. X coordinates generally describe longitudinal data, Y coordinates describe latitudinal data, and Z coordinates typically describe an elevation. Not all GCSs are the same once projected on a map because they are based on different datums that allow for specificity in mapping.

Geographic Coordinate Systems must be defined by a datum, which are sets of reference points on the Earth’s surface. Because there are literally an infinite number of ways to view the Earth, it is critical to account for distortion in specific areas. For example, if we are studying the dispersion of moose in Alaska then we would likely not want to use the same datum in a study of kangaroo in Australia. Using specific datums allows us to get the most accurate depiction of the location that we are studying.

Generally, GIS programs such as Cartographica can quickly translate datums if they are originally projected on different or non-specific datums.

A common translation that users might encounter is if data isn't projected using the WGS 84 datum. WGS 84 or World Geodetic System (1984), is a standard datum for many GIS and GPS devices, and is the only world wide datum. A user that brings in data collected from a GPS device and then attempts to map the data with a specific datum, might find that their map is not accurately projected. Cartographica can account for this by translating data to an already established datum like WGS 84. We have incorporated NTv2 support to provide accurate mapping between NAD27 and NAD83.