Geographic Information System (GIS) - Terminology (Continued) - Projection
The Earth is curved and maps are flat. The process of flattening out the Earth onto a flat piece of paper or computer screen is a mathematical process called a projection. No matter how you try, the resulting maps always have distortions. There are four types of distortions that map makers consider
- Conformality - are the shapes of the map features accurate
- Distance - are the distances measured on the map accurate
- Area - are the areas represented on the map proportional to their true area on the Earth
- Direction - are directions between points on the map accurately represented
There are many type of map projection. Some score well on one or some of the above attributes and others are an attempt at getting the best compromise on all four. Take a look at the following map of the world, made using the well known Mercator projection.
Compare it with the following map made with a Mollweide projection. Look at the relative sizes of Africa and Greenland in both maps.
Africa is 14 times the size of Greenland. The Mollweide projection accurately represents areas, whereas the Mercator projection exaggerates the areas as you get closer to the pole. However, the Mollweide projection shears the shapes near to the poles.
The azimuthal equidistant projection provides a compromise between conformal and equal-area projections.
