What makes a good map? When done well, a map is a vehicle for effective communication. There are many cartographic principles to help guide effective map making. Below are ten common considerations that all cartographers should incorporate as part of their map making process. This list isn’t meant to be a comprehensive list but rather a starting point of things to contemplate. Different cartographic presentations will require additional points of consideration and techniques.
1. Geographic Bounds
The extent of the geographic area mapped will affect a whole slew of cartographic choices from the map projection used to data and symbology choices. The geographic area of the map should be restricted to the extent of the map’s subject data.
2. Background Data Elements
There are two main reasons to include data on a map: to support the subject matter of the map and to provide orientation (e.g. streets, cities, points of interest). It’s important to choose data that is relevant and current to the map. For example, choosing an out of date street layer for an area that has recently undergone change can be confusing. Cluttering the map with too much background data can lead to excess noise and dilute the actual message of the map.
The choices of symbology can make or break a map. The color choices, line widths, icons, and labeling (more on labels next) all affect the readability, and hence message, of the map.
Consider the intended audience of the map when selecting design choices. A map aimed at children might involve brighter colors and less complexity in the symbology. A general audience map might involve the use of laicizing terminology. A map with a potentially color blind audience should not contrast certain colors.
While it may be tempting to label all features shown on a map, doing so can block underlying features, create a cluttered looking map, and create confusion.
In the example below, the use of labels creates a lot of noise on the map. The use of what feels like every label type clutters the map, making the map hard to read. The labels overlap and cover the roadway network, making it hard to see the actual data on the map. Labels should be used sparingly to identify important aspects of the matter. Since the map below was created to show the major roadway system, only major cities and regions should be labeled.
While the proliferation of customized Google Maps has contributed to the democratization of GIS data creation, it has also resulted in a slew of maps either no legends or poor legends. Legends are the key used to decipher the symbology on the map. They need to be legible, not overly cluttered, and easy to understand.
When color ramping is used, care must be taken to using colors that are easily discernible from each other with the naked eye. In the legend below, the color ramp for uses color shading that makes it difficult to differentiate one Australasia ecozone from another.
6. Incorporating Map Elements
Making sure that all map elements are properly applied is important for providing readers with the context of the map. Most maps should have a clear and concise title, a notation on the scale (or if the map is not to scale), and, when needed for orientation, a north arrow. Some cartographers may disagree with the need to always include the north arrow and scale bars and while I can lend validity to the argument that some maps are obviously oriented north (that of course, assumes that the viewer north orientating abilities are on par) or are at the global level in a projection that makes a north arrow impractical , I agree with Jon Zeitler, Science and Operations Officer at the National Weather Service Forecast Office’s position that “[t]he addition of a north arrow can never harm a figure, only help with clarity.” For more about the debate on using a north arrow, read “To North Arrow or Not to North Arrow“.
All maps should document all sources of data, currency of those datasets, and any other information helpful to the viewer. Also include the map projection and datum used. Lastly, be sure to add the author of the map so that the map can be properly referenced in other documents.
8. Map Layout
Choice in map orientation (portrait versus landscape) and placement of map elements affects the visual appeal of the map.
9. Locator Map
Unless the map is aimed at a very specific knowledgeable audience or is of a geographic breadth (such as a countrywide map or a global map), it can be very helpful to include a smaller inset map showing the location of the mapped area. This helps to further orient the viewer in placing the geographic context of the map.
10. Peer Review
Another set of eyeballs on a map, especially a critical one, should automatically be a part of your cartographic process. Peer review on documents is a common practice, yet a lot of GIS professionals and cartographers toil in isolation. Created a trusted and respected circle of peers that can collectively review maps and provide constructive feedback. The forum CartoTalk is also a great place to ask for feedback on maps.
Article first written: September 10, 2011. Last Updated: September 13, 2011.