The demarkation between land and a body of water can be enhanced cartographically through the use of coastal vignettes. From a cartographic perspective, a coastal vignette is a way of displaying water so that areas closest to the shoreline are displayed with a white color. The water is then color ramped so that the color becomes gradually darker as the distance from the shoreline increases. The general idea is to roughly mimic that, in general, water tends to be deeper the farther one travels from the shore. The resulting cartographic effect provides the illusion of an added dimension to an otherwise flat map.
There are different techniques that can be employed to create coastal vignettes using vector-based or raster-based approaches. One easy method is to create multiple ring buffers and color ramp based on distance. The first step would be to create buffers around the landmass. In your mapping software, access the multiple buffer ring function and set up the landmass to be buffered for a select number of rings and set the distance. Make sure the option to dissolve the rings is select. When setting up the multiple ring buffer function, two parameters need to be considered. The first is the distance between the rings. The closer the buffer rings, the smoother the color gradation will appear. The second consideration is the number of rings. The more buffer rings, the further the distance from the shoreline that coastal vignettes can be shown. In the first map below, the buffer was set at intervals of 5,000 meters. In the second map below, the interval was set at 1,000 meters. Note how much smoother the color gradation is on the map with the smaller buffers.
Depending on the cartographic effect desired, different intervals and number of rings will be called for. Further limitations will also be the drain on your computer’s resources. A high number of rings will take longer to draw and will increase the size of the map, constraining either your printing options or the size of your map image. If a smooth effect is desired, the best option is to create a multiple buffer ring with a small number of rings (under 25 rings) with short intervals and then set the background of your map or the water layer to the darkest color in your color ramp. That way only the immediate area next to the shorelines is color ramped and the water areas farthest from the shoreline are colored by the background color and blend in with the coastal vignettes.
- Vector and Raster Methods for Creating Coastal Vignettes – Esri White Paper (also check out the Symbolizing Shorelines blog post in the Mapping Center which has some downloadable sample files to experiment with)
- Classic Cartography Techniques in ArcMap – PDF from the Yale Map Collection of cartographic techniques including two coastal vignette techniques.