6.2: Map Communication

The International Cartographic Association (ICA) defines a map as “a representation, normally to scale and on a flat medium, of a selection of material or abstract features on, or in relation to, the surface of the Earth.” In other words, maps are an approximation, a model, a summary of the real world.

Maps communicate; they represent and help us organize knowledge by representing a portion of the Earth’s surface. They are created for transmitting spatial information to a map reader, yet most maps are improperly designed and do not communicate easily nor effectively. This is not the fault of the map reader. The fault lies with the cartographer that makes the map. To design better maps, consider the cartographic communication process with its four stages (see Figure 6.2): 1) Real World, 2) Selection, 3) Generalization, and 4) Map.

Figure 6.2: Cartographic communication process.

Real World

As described in Chapter 1, the world is too complex for direct analysis and understanding, so we create models of the world by selecting and generalizing some of its features. Imagine, however, if we could record the world’s infinite detail on a map. Lewis Carroll, author of Alice in Wonderland, described such a detailed map in Sylvie and Bruno Concluded. In this fantasy, a Professor explains to another how his country’s cartographers experimented with ever-larger maps. The Professor states, “And then came the grandest idea of all! We actually made a map of the country, on the scale of a mile to the mile!” “Have you used it much?” the other person enquired.” No, says the professor, “It has never been spread out” … “the farmers objected: they said it would cover the whole country, and shut out the sunlight! So we now use the country itself, as its own map, and I assure you it does nearly as well.”

In reality, the “country itself” is a poor replacement for a map. If we could use the real world as our guide, then we would not need maps. Every map selects and generalizes the world’s features, and these little “white lies” help maps communicate.

Selection

Maps are selective. You determine what should be, and equally important, what should not be included on your map. If features do not aid your map’s purpose, nor orient the map reader, eliminate them. There must be a reason for the presence of every feature type. Guiding your selection process should be two essential considerations: the map’s purpose and its scale.

What is the purpose of your map? What are you trying to get across? Who is your audience? Addressing these questions helps you determine how much detail should be placed on your map. Selecting too many types of features obscures your map’s primary purpose.

Scale is the relationship between distances on the map (or screen) and corresponding distances in the real world. It is a major factor in determining which features are selected and which are omitted. Ask yourself, how is the map going to be presented to your audience? Will it be on an 8 ½” x 11″ piece of paper, a 3″ x 3″ portion of a newspaper, or through a data projector onto a screen? The physical size of the presented map largely dictates the amount of detail that can be displayed on the map. The chosen scale affects not only the selection of features but also the degree of their generalization.

Generalization

Geographic data and detail are without limit. If you are flying high above a city, you will see certain features that define the city’s overall shape and its major neighborhoods. As you descend into a neighborhood, the homes, streets, parked cars, and sidewalks become clear. Descend into a backyard and you see a pool, a vegetable garden, chairs, and a redwood deck. Dogs and cats are visible. Pull out a magnifying glass and investigate the redwood deck’s grain to see its color, pits, splinters, and undulations. To capture all of the real world’s features and their detail, you would need an infinitely large database and an infinite amount of time.

The features you select need to be generalized, but how much detail should they have? Map size being equal, large-scale maps that depict features in a small area can have more detail. Here are several generalizing tasks to make map reading easier and more effective:

1. Smooth features. For example, take some kinks out of a river or a road. Beck’s London Underground map (Figure 6.1) smoothed and straightened subway routes, which made the network more intuitive to map readers.
2. Abstract features. Detail catches the map reader’s eye. Abstraction removes detail. Remove the detail of a city’s street to a single line. For example, represent the library’s actual footprint with a black square.
3. Aggregate features. Some features may be lumped together to deemphasize them. For example, represent several school buildings with a single symbol.
4. Exaggerate features. While smoothing, abstraction, and aggregation seek to deemphasize features, exaggeration places greater emphasis on the feature. If it is important for the purpose of your map, enlarge the feature.
5. Displace features. Sometimes features need to be moved, perhaps slightly, to accentuate them and make the map more visually pleasing and intuitive. For example, Beck moved London’s train stations.

The primary role of maps is to communicate, and this is impossible without selection and generalization. Still, people have difficulty reading maps. If you find maps easy to read, it is partly due to your familiarity with maps and their conventions. Once you understand these conventions, map reading becomes easier and reinforces that understanding.

Conventions, a form of abstraction, are signs and symbols that allow people to read maps. Cartographers rely on conventions for good cartographic communication. Some conventions are almost universally understood like the use of blue for a river’s line work and to fill a body of water. Most adults comprehend that water is symbolically represented by blue. Even on maps with text in foreign languages, you can distinguish water based largely on color. Lines on a road map are another example. They are easily understood as roads even though they have no width, lanes, curbs, or gutters.

Universal examples, however, are rare. Culture and profession influence how one interprets conventions. For example, red, which symbolizes danger (traffic lights and fire for example) and anger in Western countries stands for courage, happiness, success, and Communism in China. The greatest number of conventions, however, comes from professional associations, which have developed complicated formal and informal symbols. For example, geologists use both solid and dashed lines with associated symbols to infer normal faults, strike-slip faults, thrust faults and their associated characteristics like foliation, bedding, and lineation.