Understanding distortion

In this topic, we'll look closer at spatial properties and how they are distorted in projections. We'll pay special attention to Tissot indicatrices as a technique for assessing distortion on a map.

Remember the four spatial properties that are subject to distortion:

· Shape

· Area

· Distance

· Direction

No map can preserve all four. (Only a globe can do that.)

Some maps preserve one property, and some preserve two, but none preserves more than two. Some maps don't preserve any properties perfectly, but compromise a little bit on all of them.

If a map preserves two spatial properties, one of them is always true direction.

Any spatial property can be preserved alongside direction. Direction and distance are preserved in the Azimuthal Equidistant projection. Direction and shape are preserved in the Stereographic projection. Direction and area are preserved in the Lambert Azimuthal Equal Area projection.

The following properties can't be preserved together:

No property can be preserved along with a property other than direction. There are no conformal equidistant projections, no equal area equidistant projections, and no conformal equal area projections.