There are lots of ways to indicate water on a map with lines – and many more with tone or colour. Here are four I regularly use.
1. Broken Waves
After you have your coastline, use short, gently curving lines along the shore. The lines should follow the shapes of the coast, but smooth out the kinks. Close to the shore the lines should be closely packed, and should follow the details of the coast closely. As you move further from the coast the lines should come further apart, they should be longer, and they should follow the form of the largest features of the coast. For a great example of this style – see maps by Mike Schley
2. Depth Contours
In this case each ripple is a single continuous line. This gives the impression you are indicating depth – and harks back to the style of nautical charts. There’s lots of tutorials out there that suggest you select your land mass, expand the selection and stroke, then expand again and stroke, and so on. I don’t like this approach because it introduces artifacts that make it obviously computer generated. Also, the uniformity of the distance between lines is utterly opposite to any real depth lines. It just looks too generated. Hence I stick to hand drawing.
This is a much more stylised coastline. First of all I add a single solid line around the coast. This gives some distance between the coastline and the pattern. The white space here adds important definition to the coast.
With that in place I use short dashes to indicate waves. They are continuous near the shore, and break up to short lines further away. By adding more white space further from the shore it fades out the pattern – which looks great from a distance. Don’t worry about being too careful with the dashes – but do try and keep the lines of the pattern horizontal. Use very broken lines far from the coast to spread the pattern into the deep water.
4. Simple Lines
This is the most abstract. Here the lines are just horizontal. As with 3 they don’t touch the coastline – to keep that white space. The lines are the best by the coast, and taper as they get further away. It’s a quick style, and surprisingly effective. But it only works for some map styles.
That’s all for this one – pitch in with questions or suggestions on other mapping topics.