An earlier post explored ways to draw (or “symbolize” to use cartographer-speak) a shoreline in a monochrome map. A new style has some across my desk, suggesting it is time to revisit the topic.
The basic problem is how to communicate to a map reader both where a shoreline is located and which side of that line is land or water. One approach is to shade the land or water a medium gray. I’ve talked about this in a couple of earlier articles, exploring techniques that can be used with both GIS or drawing software as well as those that work with hand-painted ink wash. Shading creates some problems, however. Map users do not agree on whether the land or the water should be shaded, so there is a risk of confusing map readers. In addition, gray shading is often not handled well by printers; the gray that looks good on a computer screen can appear as much lighter or darker when printed. As a result, there is a lot to recommend techniques that rely not on shading but only on one-color lines. Some very traditional ways follow.
Stippling, or using little dots, to show the land adjacent to the shoreline. This technique has a certain intuitive clarity. The stippling creates a shaded effect for the land, suggesting that the entire land area is slightly darker than the adjoining water area. In addition, the stipples suggest a sandy shoreline, so hint to the map reader the presence of a shoreline. Of course, any suggestion of sand can also be a problem in places where sandy beaches are not present. For a map reader on the rocky coast of Maine, for example, a suggestion of sand is more confusing than helpful. Here is an example of a pen-and-ink map that uses stippling, plus a few little tree symbols to further indicate which side of the line is land.
Another technique is to use small line marks to indicate the shoreline. One style, popular in pen-and-ink maps a century of more ago, is to use a simple dash-dot-dot symbol along the shoreline. The dashes are drawn horizontally on the page, projecting from the shoreline into the water area. These marks have a nice intuitive appeal: they seem to suggest water getting deeper along the shoreline.
Another line technique is to draw fine lines parallel to the shoreline on the water side. Like the dash-dot technique described above, this was also popular in pen-and-ink mapping a century or more ago, but still has intuitive clarity today. Typically the space between the parallel lines increases as distance from the shore increases. Often the outermost lines are drawn with a thinner pen.
The technique of drawing lines parallel to the shoreline can be done with mapping software as well as pen-and-ink. The technique can be a bit tedious, even with software tools. Typically it involves creating “buffers” on one side of the shoreline, then symbolizing those buffers with a fine border. Here is the output from QGIS software:
The sailors and authors Lynda and David Chidell used a superb combination of techniques in their book Cutting the Dragon’s Tail. They stippled the land side of the shoreline, then used very subtle parallel lines on the water side, particularly around headlands. This subtle use of the parallel lines has even greater intuitive appeal than uniform parallel lines because is suggests waves breaking around headlands. Note as well the typeface that suggests the kind of lettering used on nineteenth century maps. With many thanks to David and Lynda Chidell for permission to share their work, the map follows.
Their technique can be adapted to larger scale maps (i.e., those showing a smaller area), as shown in this map of the same small Maine bay with which this discussion began:
This collection of different ways of showing something as simple as a shoreline lead to one worthwhile closing theme. In the cartography-speak, it is “redundant symbology.” In straightforward language, it is the idea that different people respond to different visual cues, so it’s a good idea to communicate the same information with more than one visual technique. For some people, some kind of shading will jump off the page as the difference between land and water. For others, parallel lines might be so evocative of waves lapping on a shore that they are the obvious clue to which side of a line is land and which is water. So, whenever it is possible to provide more than one visual cue without making the map too busy or distracting from other important information on the map (an important topic for another day), do it.