As a cartographer, one of your goals should be to concentrate distortion (whether of area, angle, distance or direction) in portions of the map that are not important (or are less important) for the map’s intended use. One way of achieving this goal is to customize a projection by centering it so that there is the smallest amount of distortion in your area of interest. Areas near a map’s center line or center point are the areas that will contain the smallest amount of distortion of any type. You can customize a projection by specifying an alternate standard line or point.
Consider the following scenario. You are asked to produce a map showing the volume of goods that are shipped on particular routes from ports in Asia to Los Angeles, California. By default, the central meridian for most small-scale projections is the prime meridian, which runs through Greenwich, England. If we choose to center our projection here, we have centered a most extreme type of deformation (tearing) right through the area we are most interested in (the Pacific Ocean; see Figure 7.cg.12, below)!
We can easily improve the projection for our purpose by centering it at a more appropriate location: -140° (see Figure 7.cg.13, below).