One of the major Major MAJOR problems that bad maps have is a lack of sufficient figure-ground contrast. Let it be impressed on the new cartography student that there is almost never a time when there is too much contrast. You pretty much can’t go wrong when it comes to lightening up the background features in order to make the foreground more prominent. Rule of thumb: think that hillshade is light enough? Try 10% lighter.
Gestalt is a general term that describes a group of objects (physical, biological, or even psychological phenomena) that have a definition as a group that is different from their definitions when they are apart. This concept, borne of German psychologists in the early 1900s, when applied to graphic design, encompasses many concepts including image continuity, closure, similarity, and figure-ground. For the purposes of this discussion, we are interested primarily in the gestalt concept of figure-ground of course, which refers to the differentiation between an object and its background. GIS maps usually include objects that need to be emphasized and separated from the other objects on the map even though the other objects are also important for geographic context. This applies to feature pairings such as land and water, city points and land, or watersheds and forest stands.
In this map slice, we’ve got a National Geographic basemap at full saturation underneath future areas to be sewered in red-dash and ages and locations of existing septic systems as different colored dots (red is greater than 30 years old).
Nice basemap but insufficent contrast with overlay data
Increasing the transparency by quite a bit helps the data come to the forefront. You can increase the transparency in ArcMap by double clicking the basemap layer and setting it to about 50% in the layer properties > display tab. Here, I’ve actually done it in Inkscape, with the filter > transparency utilities > light eraser tool. The same thing can be done in CartoCSS, PhotoShop, QGIS, or whatever your GIS demon is.
Much better figure-ground contrast here
But we can go even further, increase the transparency to 60% or, in Inkscape by using the light eraser filter once again, and really achieve a nice looking contrast:
Even better contrast
Pre-rendered basemaps have never received the hype that they should have. They’ve made the workflow of the GIS Analyst a thousand times more productive, in my mind, since they first appeared. Even if you don’t use ArcMap you still have a wealth of pre-rendered basemap components available to you via Natural Earth Data and other sources. The main point here is to re-iterate the importance of making sure that basemap data is indeed “basemap data” by visually lessening its impact on the map while still retaining its efficacy.
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