As with statistics, graphs, and other visual representations of data, it's important to examine the content of a map closely. Subtle details, generalizations, and personal perspectives all impact the viewer's interpretation of what the map portrays.
In his book, How to Lie With Maps [i], geographer Mark Monmonier provides users with guidelines to help them read maps critically. Some of these tips, along with others from TOXMAP, are listed below.
Remember that not all maps are made by professional cartographers. Today's image and cartography software have made it possible for non-cartographers to create and design maps that may hide or obscure features that many users would expect to find.
Keep in mind that when portraying a three-dimensional world via a map, the geographic region that the map represents may in some ways be changed or distorted. For example, map symbols are often "thicker" or larger than the elements they depict.
Don't forget that not all maps are designed to inform the user about a location or geographic region. While some maps are symbols for geographic knowledge, others are created just for "looks," with less or little attention to accuracy.
Pay close attention to the map legend and to the symbols used on the map. For maps that use color-coding to represent ranges of data values, note how the ranges are determined and how data are categorized within.
Learn as much as possible about the data depicted on the map. When was it created? Was it summarized or simplified in some way before being used?
Know that everything on a map can be considered "data" and deserves whatever attention is relevant to your work. For example, a map might use accurate data to represent large rivers and bodies of water, but have incomplete or out-of-date representations of streams, ponds, tributaries, and other small water features. While this map might be useful for the casual user, someone concerned with local flooding or wildlife would likely need better water resource data.
Think as much about what isn't shown on the map as what is. Are there geographic features such as mountain ranges that, if shown, would improve your understanding of the map?
