I’ve been critiquing a lot of maps lately and keeping notes on common pitfalls as well as ways to earn extra viewer “points”. * Here are those notes. Keep in mind that the maps that inspired these recommendations were all of a specific type. This means that the list of pitfalls and extra points is certainly not exhaustive.

PITFALLS

• Watch out for region boundary lines that are too thick. If you have country outlines on a world-wide map or state outlines on a country-wide map, for example, make sure they are visible, yet not overwhelming. You can make them white if the background is dark or gray if the background is light. Make them just thick enough to be visible.
• Labels should not cross lines where possible. If it can not be avoided, try putting a halo around the label to obscure the line underneath the label. If the line shows up underneath the letters it gets muddled up with the typography.
• Be wary of your font choice in large blocks of text. If there are more than two lines of text grouped together with more than, say, five words on each line, a serif font is a fresher choice than a sans-serif. If insisting on a sans-serif then look for something with a bit of flow and character.
• Run the map by someone else and ask them to tell you if there are enough labels on the map. For example, you might think everyone knows that the inset map shows Hawaii but not everyone does.
• Try not to have more than five gradations of a symbol size. This is because it is difficult for the human eye to discern differences in symbol sizes at a greater number than that. Think about how hard it would be to determine what a certain circle means if there are 12 different circle sizes on the map. If you really want that many circle sizes, then make it clear that the viewer doesn’t need to know what it represents exactly by making the legend reflect that. This can be accomplished by only showing the smallest symbol size and the largest symbol size with a line in between, for example.
• When using circles to pinpoint a great many locations on a map, don’t use circle casing (the extra bold circle outline) as it just adds clutter. If there are only a few locations and you need some extra pop then it is acceptable.

EXTRA POINTS

• Dig in to the details of the data you are portraying. If you can unearth some conclusions that aren’t readily apparent via the spatial representation, then consider illustrating these via graphs or extra text-blocks.
• If your map makes someone else say, “Oh, how neat” then you’ve probably done a good job.
• If there are large areas of a single color taking up more than 1/4 of the page, consider using a gradient fill. For example, a map of Colorado historic sites could incorporate a brown background that starts out darker at the northern border and ends up lighter at the southern border. (Make it subtle.) Of course there are lots of other ways to do backgrounds including subtle hillshading and aerial imagery but keep this one in mind too.
• You get major extra points for highly skilled incorporation of the margin elements. Think graphic-design. Sure, it is good to evenly distribute and group elements around the main map. But it is even better if those elements become a part of the overall feel rather than just hanging out around the main event. I’m thinking of unique style choices like copyright text that curves around the globe, a legend that blends in to the border, and such. If you don’t have any ideas of your own then make an effort to look at several maps on the Web, noting unique style choices that you could use.

*Pitfall! was a very succesful Atari game made by Activision. The main objectives were to keep from falling in quicksand, water or tar pits by swinging on jungle vines and earning extra points by collecting treasure.