Projection in GIS
Why do we need projection?
What is map projection? Why do we need map projection?
A projection displays the coordinate system and your data on a flat surface like paper or a digital screen. Mathematical calculations are used to convert the coordinate system used on the earth’s curved surface to one for a flat surface.
The 3D globe must be transformed to create a flat 2D map. Image retrieved from gistbok.ucgis.org.
The surface of the earth is round or a sphere (3D). However, the surface of the paper is flat (2D). So, how would you be able to transfer information on the earth to a piece of paper? It is more complicated to transform the location directly. Imagine yourself peeling an orange and observing how the location of each dot in the orange is dispersed. The properties of the orange skin are distorted.
Therefore, a Coordinate Reference System (CRS) or Spatial Reference System (SRS) is needed to transform the real places on earth into a 2D paper. This exercise is made possible by using coordinates.
Families of Projection
There are three main families of projections.
- First is cylindrical projection. This projection preserves the distances or areas.
- Second is conical projection. It preserves angles.
- Finally, the third one is planar projection. It preserves distances.
Types of Projection
There are three types of projection, namely North America Datum, WGS84 and Ark1960 Datum.
The most common method of coordinates system would be using longitude and latitude. Universal Transverse Mercator (UTM) is based on longitude and latitude. WGS-84 is an example of a UTM projection.
Choosing the correct projection depends on your location. For example, if you are located in the United States of America, you’ll use North America Datum; in Europe, you’ll use WGS-84. And in places near the Equator, you’ll use the Ark 1960 Datum.
It would help if you decided which projection you want to use before starting your GIS project. Use your country’s projection.
You may find further reading on projection in this article – A classification of map projections
Geographic Information Systems (GIS) in the Built Environment
Geographic Information Systems (GIS) in the Built Environment
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