The Role of Colors on Maps

Cartographers use color on maps to represent certain features. Color use is always consistent on a single map and often consistent across different types of maps made by different cartographers and publishers.

Many colors used on maps have a relationship to an object or feature on the ground. For example, blue is almost always the color chosen for water.

Political Maps

Political maps, or those that show government boundaries, usually use more map colors than physical maps, which represent the landscape often without regard for human modification, such as country or state borders.

Political maps often use four or more colors to represent different countries or internal divisions of countries, such as states or provinces. Blue often represents water and black and/or red is frequently used for cities, roads, and railways. Black also shows boundaries, with differing types of dashes and/or dots used to represent the type of boundary: international, state, county, or other political subdivision.

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Physical Maps

Physical maps use color most dramatically to show changes in elevation. A palette of greens often displays elevations. Dark green usually represents low-lying land, with lighter shades of green used for higher elevations. In the next higher elevations, physical maps often use a palette of light brown to dark brown. Such maps commonly use reds, white, or purples to represent the highest elevations shown on the map.

It is important to remember that on maps that use shades of greens, browns, and the like, color does not represent ground cover. For example, showing the Mojave Desert in green due to low elevation doesn't mean that the desert is lush with green crops. Likewise, showing mountain peaks in white does not indicate that the mountains are capped with ice and snow all year long.

On physical maps, blues are used for water, with darker blues representing the deepest water. Green-gray, red, blue-gray, or some other color is used for elevations below sea level.

General-Interest Maps

Road maps and other general-use maps are often a jumble of color, with some of the following schemes:

• Blue: lakes, rivers, streams, oceans, reservoirs, highways, and local borders
• Red: major highways, roads, urban areas, airports, special-interest sites, military sites, place names, buildings, and borders
• Yellow: built-up or urban areas
• Green: parks, golf courses, reservations, forest, orchards, and highways
• Brown: deserts, historical sites, national parks, military reservations or bases, and contour (elevation) lines
• Black: roads, railroads, highways, bridges, place names, buildings, and borders
• Purple: highways, and on U.S. Geographical Survey topographic maps, features added to the map since the original survey

Choropleth Maps

Special maps called choropleth maps use color to represent statistical data for a given area. Typically, choropleth maps represent each county, state, or country with a color based on the data for that area. For example, a common choropleth map of the United States shows a state-by-state breakdown of which states voted Republican (red) and Democratic (blue).

Choropleth maps can also be used to show population, educational attainment, ethnicity, density, life expectancy, the prevalence of a certain disease, and much more. When mapping certain percentages, cartographers who design choropleth maps often use different shades of the same color, producing a nice visual effect. For example, a map of county-by-county per capita income in a state could use a range of green from light green for the lowest per-capita income to dark green for the highest per-capita income.