Why can a map have all the correct information on it and still be hard to read? Overcrowding is the result of having too many roads, boundaries, labels, symbols, and other embellishments competing for the available space. Even if no element is wrong, it is still difficult for the reader to determine the main route, the main location, or the overall spatial pattern. Simplifying the map does not mean omitting any important information. It means figuring out which elements are helping the reader understand the map’s message, and which elements are just getting in the way.
Start with the purpose of the map, and let that drive all your decisions. A park map for visitors should have the main entrances, major routes, facilities, and prominent features. It probably shouldn’t show every small boundary, trail, or contour line. A map showing the population distribution across districts should show area shapes, boundaries, and symbols, but it doesn’t need to show the outline of every building. If the purpose of the map isn’t clearly defined, you will be inclined to keep any and all elements that you have data for.
Make sure the visual hierarchy is working properly. If every feature is presented with roughly equal emphasis, nothing stands out. Heavy-weight local roads compete with lighter-weight highways, heavy-weight district boundaries compete with light-weight area fills, large-scale point symbols cover up the nearby labels. The most important information should be the most heavily weighted, and everything else should get progressively less emphasis by decreasing the line weight, color saturation, or symbol size. Base-map elements should be present as context, but shouldn’t be so heavy that they draw more attention than the primary map elements.
Another cause of overcrowding is the labels. City names can overlap features, labels can run across boundaries, and labels can be placed too close together. Instead of reducing the size of all the labels to the point of illegibility, consider removing any labels that aren’t critical to understanding the map. Try moving the labels around roads and other features, maintain a consistent labeling style within each type of label, and only use one label even if multiple occurrences of that feature exist. A small number of well-placed labels are easier to read than a full set that results in a gray smudge.
For some practice, copy a crowded map, or make two maps of the same area, and leave the first one unchanged. For the second map, remove any minor roads, reduce the weight of the heavier lines, merge categories together, and only include those labels that are needed to understand the map. Stop and zoom out after each couple of edits to see if you are overediting, and whether the features you just deleted were really needed. Zoom out further to the scale at which the final map will be viewed to make sure the changes are appropriate.
The legend should be simplified along with the map itself. Removing a category from the map without also removing it from the legend leaves the reader wondering what to do with that legend entry. Merging several categories together might require a new common label. Changing the color or pattern of a symbol requires the same change to be made to the legend entry. Remember that the title, legend, scale bar, north arrow, and source note also take up space, so plan where those will go before cluttering the map with features.
There are some easy signs of success. Show the map briefly to someone who hasn’t seen it and ask them what they notice first. They should identify the same feature that was the purpose of the map. If they instead notice a minor boundary or a decorative symbol before the purpose of the map, reduce that feature again. The next time you feel like a map is too crowded, don’t immediately reduce the weight of all features; try removing one feature and see how much better that makes the remaining ones.
