Now in its fourth year, Azavea’s Summer of Maps Program has become an important resource for non-profits and student GIS analysts alike. Non-profits receive pro bono spatial analysis work that can enhance their organizational decision-making processes and programmatic activities, while students benefit from Azavea mentors’ expertise. This year, three fellows worked on projects for six organizations that spanned a variety of topics and geographic regions. This blog series documents some of their accomplishments and challenges during their fellowship. Our 2015 sponsors Esri, Temple University Geography and Urban Professional Masters Studies Program and Betsy and Jesse Fink helped make this program possible. For more information about the program, please visit the Summer of Maps website.
There is less need for reference maps or road maps since the recent ubiquity of technology like Google Maps and smartphones. Sometimes however, a reference map or base map is just what you need in order to provide context for complex spatial information. Reference maps are large format maps that contain many layers such as streets, water features, towns, and land cover types. These layers often overlap and need customized labeling. This can lead to very cluttered maps if not styled and classified properly. Below are a few tips to manage base map features without distracting from the information presented.
Not all roads are created equal. Displaying a highway as the same color and line-width as a residential street is not only misleading, it makes maps more difficult to understand. Try to classify features similar to how you might classify data in a thematic map. Some street data is already classified with each line segment having a numerical value with 1 being the highways and higher numbers being smaller streets. If the data is not pre-classified, there is often a “Speed Limit” field which can function in the same way.
It is also important to classify water features as many datasets contain not only major rivers, but the tributaries that feed into them. This can easily take up more space than necessary on a map. Most hydrology datasets have a field for the type of water feature broken down into rivers, streams, and tributaries or a a numerical classification similar to the streets.
Data can be styled with different line-widths and colors based on importance after it has been classified into a distinct hierarchy. Warm colors such as red or orange are often used to represent highways because they give off a feeling of speed and urgency while showing major connections, whereas smaller roads use black or dark gray. Depending on the scale of the map, it may also make sense to remove some lower-order features from the final rendering. Always try to avoid default color selections and use your own palette. Colourlovers.com is a great website for viewing and sharing unique color palettes, and the always-reliable ColorBrewer2.org.
Fitting hundreds of labels on a single map can be tricky, but classified data can help. Highways can be labeled with route numbers inside of a state road or interstate symbols rather than using text alone. For smaller features, be sure to use a smaller sized sans-serif font (avoid fonts with any embellishment) to improve legibility. Also try to avoid using halos around the text–only use a very thin one if necessary.
Cartography relies heavily on hierarchies to communicate large amounts of information. When ordering the layers on your map, place layers that fill up the most amount of space, such as land cover or topology, at the bottom of the layer stack. Place layers that take less space, such as streets, point data, or town borders on the top of the stack. The order should look something like this from bottom to top:: land cover, topography, hydrology, streets, building footprints, administrative boundaries.
Above is a small piece of a reference map I created this Summer that follows all of the guidelines I just mentioned. I made U.S. Route 1 red with a thin black outline and the neighboring state route 141 orange to highlight the major connections in the area. The rivers and streams are the same color, yet I only labeled the features that were classified as rivers. The town labels are a simple Arial font with no halo, however I did use a slight drop shadow to distinguish it from the multicolored background. The town borders are polygons with a dashed gray line and no fill. Lastly, the layer order goes from bottom to top: land cover, hydrology, roads, and administrative boundaries.
Below is a low resolution image of the entire map (as the full map is too large for this blog). You can explore the entire map (67 MB in size) at this link. Even in the smaller map below, you can still see U.S. route 1 along the coastline. When making your own base maps, keep these tips in mind and think of your map like a painting with a background and a foreground. Always make a distinction between features that you want people to notice and features only included for context.