One of the biggest challenges that cartographers face is clients who ask for maps containing every layer under the sun. Often, the project starts out as a map with a single focus but as it progresses the client asks for more and more layers. So “make a map of nitrogen hot spots” becomes “make a map of nitrogen hot spots with bathymetry and docks and populated places and nearshore septic systems.”
This is all well and good except for the fact that rarely are you given enough time to make this all happen without the result being a confusing mess of points, lines, and polygons. And this happens with traditional static maps as well as web maps. In fact, web maps can be even more difficult because certain engineer-types will request 20+ layers — most likely every layer your organization has ever produced — be placed on the same map.
The problem lies with (1) The symbology conflicts that inevitably arise when trying to create a distinct color or pattern for all 20 layers, many of which will have their own sub-characterizations and (2) the 20+ layer interactive map that the engineers wanted is not at all what the public wants or is able to understand, though often both engineers and the public are given the same web map interface.
To be sure, it is possible, especially with static maps, to create a map with many layers of information that looks good. However, one must realize that these are most often created by large companies with many resources, including generous timelines and many personnel. The decade-old topographic atlas of Washington State that’s on the bookshelf in my office has 71 different point, line, and area symbols listed in its legend, all of which come together in a cohesive and meaningful manner in the maps themselves. The atlas is made by DeLorme, a sizable company by all accounts. Hey, it even has a humongous rotating globe at its headquarters.
So what is a cartographer to do when faced with requirements to place a large number of layers on a map without the resources of a large company like DeLorme? Some options include:
(1) Manage expectations: let everyone know at the outset that you will do your best to incorporate as much meaningful information as possible but will reject requests for additional layers when those layers conflict with the original intent of the map.
(2) Create multiple maps: adopt a small-multiples style of mapping so that everyone’s favorite layer gets shown, just not all at the same time. This is possible in web maps by creating a “metro tiles” type of interface linking to the separate maps. Even just creating two maps, one for the public with only the most salient layers and one for the engineers with everything but the kitchen sink, could alleviate some of the design pain.
(3) Employ a detailed, yet mostly mono-chromatic pre-rendered basemap to provide all the appropriate contextual information. These pre-rendered basemaps (from Esri, Stamen, Google, etc.) look good, are ready to go, and contain a multitude of layered information.
If you are an embrace-the-challenge type of cartographer, and are amenable to trying to incorporate all requested layers into a single, effective, design, then at the very least make it known that you will need a commensurate amount of time, or even additional personnel, to complete the project.