Map elements: The usual bits and pieces
Chapter 1: Context and Concepts

Generally, maps have the following elements that help provide consistency and comprehensibility for readers.

  • A title (or caption) to describe the map.

  • A legend to interpret the content of the map, such as the symbols and colors.

  • A scale to translate distance on the map to distance on the ground.

  • Orientation12 to show compass direction.

However, a review of maps in cartography texts and elsewhere reveals the inconvenient fact that these conventions are often overlooked. Context should dictate whether some or all of these elements are included.

For example, in a situation in which maps of the same jurisdiction, or parts of it, are produced and distributed to the same audience on a repetitive basis, a label telling readers the area would be a waste of ink. But if the map were intended for wider distribution to audiences that might not know what they were looking at, a caption or heading would be appropriate. Similarly, scale may be redundant when the users of the map are educated to the spatial relationships on the map, often through years of field experience. Orientation, too, is unlikely to be critical in locally used crime maps, for which north is almost always "up." It may be worth noting that Minard's map of Napoleon's army (see figure 1.5) has no orientation, and if you want to be picky, it has no legend per se.

Indeed, a legend is perhaps the only somewhat (but not entirely) indispensable map element. Readers need to be absolutely sure what map data mean, and the legend is the only reliable guide to this information. Some maps may be so simple that a legend is not necessary. An example would be a map showing points, each of which represents a residential burglary. The heading or caption of the map (such as, "Locations of residential burglaries in St. Louis, September 2000.") can contain the necessary information and override the need for a legend.

This discussion may imply that one can be slapdash about map elements, but that implication is not intended. Careful consideration should be given to whether a particular element should be included; if an element is included, it must contain complete and accurate information. (For further elaboration, see "Map design" section in chapter 2.)

Chapter 1: Context and Concepts
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Mapping Crime: Principle and Practice, by Keith Harries, Ph.D., December 1999