Authors: Eligio Maure, Blessing Kamwi

5.4. Definitions#

5.4.1. Geodesy#

Geodesy is the branch of mathematics or science dealing with accurate measurement of Earth’s geometric shape, orientation in space, and gravity field, including the changes of these properties with time.

5.4.2. Geoid#

The geoid is an equipotential, or level, surface of the earth’s gravity field. The geoid, approximately, equals mean sea level (MSL) and generally differs from local MSL by a metre or so. It is a complex shape influenced by the composition of the earth so it may have discontinuities in its slope. This means that the geoid’s surface is analytic as opposed to a mathematical surface like an ellipsoid.

5.4.3. Ellipsoid#

About Ellipsoid

5.4.4. Coordinate Systems#

Coordinating system is a reference framework that defines locations of features on the model of the earth as latitude and longitude. Its units are usually degrees. Coordinate systems play a significant role in the way the physical systems are described. Below we described the two most important coordinate systems namely the Cartesian and the Spherical coordinate system.

5.4.5. Map Projections#

About Map Projections

5.4.5.1. Projection categories#

5.4.5.2. Azimuthal Projections#

These projections are based on a flat piece of paper touching the earth at a point.

5.4.5.3. Conic Projections#

5.4.5.4. Cylindrical Projections#

Prior to that, it is worth noting that the creation of a map projection generally involves these three steps:

  1. Selection of a model for the shape of the body being projected (a sphere or ellipsoid)

  2. Definition of a geographic coordinate transform from angular (longitude and latitude) to planar coordinates (easting and northing) or vice versa.

  3. Reduce the scale (in manual cartography this step came second, in digital cartography it comes last)