How Maps Represent the World
An introduction to scale, coordinates, projections and the choices behind every map.
A map is a model
A map is not the world itself. It is a selective representation designed for a purpose. A transit map emphasises routes and stations; a topographic map shows terrain; and a political map highlights administrative boundaries.
Every map leaves something out. The important question is whether the information it preserves is useful for the task.
Scale and detail
Map scale describes the relationship between a distance on the map and the corresponding distance on the ground. A large-scale map covers a smaller area with more detail. A small-scale map covers a larger area with less detail.
Scale affects what can be shown. A neighbourhood map may label individual streets, while a world map cannot display every road or building.
Coordinates
Geographic coordinates describe locations using latitude and longitude. Latitude measures position north or south of the equator. Longitude measures position east or west of a reference meridian.
Coordinates are useful, but they do not by themselves describe how the curved Earth should be drawn on a flat page or screen. That requires a map projection.
Why projections matter
Every flat map of the entire Earth introduces some distortion. A projection may preserve local angles, areas, distances along selected lines or other properties, but no single projection preserves everything everywhere.
The familiar Mercator projection is useful for navigation because it preserves local angles, but it greatly enlarges areas near the poles. Equal-area projections preserve relative area but may change shapes.
Choosing a map
A useful map begins with a question. For route planning, a road network and travel constraints matter. For comparing the size of countries, an equal-area projection is more appropriate than a projection that exaggerates high latitudes. For understanding elevation, contour lines or shaded relief may be essential.
Reading maps well means understanding both the information they show and the choices used to represent it.