Cartography Guide

A short, friendly guide to basic principles of map design

What is a map?

It may sound silly to ask what a map is, but it’s important to understand the what and why of maps.

A simple definition is that a map is a representation of a place. This carries two important implications that are sometimes neglected:

  1. A map is not an objective depiction of reality. It is a symbolic interpretation of place and highlights the relationships between elements in space, either perceived or actual. It reflects choices, biases, and agendas of the mapmaker. When you see or make a map, think critically about it. What does the map show, what does it omit, and why? How were the data collected and manipulated to produce the end result? Those are only a couple of things that affect how a map ultimately is interpreted by its readers.

  2. The practice of cartography is as much about removing things as depicting them. A map does not and cannot represent everything in the place. Things must be omitted, simplified, etc. for the map to make sense. This is how a map achieves clarity and usefulness: it strips away details of the world so that the map’s purpose shines through.

Types of maps

Broadly, maps fall into two categories:

Reference maps emphasize the location of spatial phenomena, such countries, cities, rivers, etc. Chances are the maps you use most in your daily life are reference maps—street maps (e.g., Google Maps) that help you see where things are. Other common reference maps emphasize physical landscapes—think topographic maps or maps of a national park.

USGS topographic maps and Google Maps are classic and modern examples of reference maps, mostly intended to show where things are.

Thematic maps emphasize the spatial pattern of geographic attributes or statistics about places and relationships between places. For example, while a reference map might show the locations of cities, a thematic map might also represent the population of those cities. A reference map might show bank locations, while a thematic maps shows average income in an area. It’s the difference between mapping places and mapping data.

This map of poverty from the US Census is a thematic map, concerned with the geography of a demographic phenomenon.