The distinction between land and ocean areas on maps is often enhanced by adding a coastline. This is particularly useful on maps where the land and ocean tones are similar, and it gives a map a much “crisper” look.
 
 
Without coastline With coastline
Although we provide paths and masks for coastlines as well as outline maps in FreeHand and Illustrator formats, creating your own custom coastline masks is particularly easy in Photoshop:
1. Having colored your map the way you want it, you may still have the mask channel. If not, open the “Channels” floating palette by selecting “Show Channels” from the “Window” menu. Click on the right-pointing arrow at top right of the Channels palette and select “New Channel.” Open the corresponding map mask, copy it, and then paste it into the channel you just created.
2. Go back to the combined RGB channel. Choose “Load Selection” from the “Select” menu.
3. Define a foreground color by clicking on the foreground color swatch in the Toolbox palette, and using the color picker or custom colors option to select a color. This will be the color of the coastline.
4. Choose “Stroke...” from the “Edit” menu. In the dialog box, enter a width of 1 pixel, and check the “Outside” radio button. Experiment with these three options, to see which method suits your image best. Leave the other settings as they are. The width of line you choose will depend on the resolution of map you are working with – 1 pixel is fine for 72 dpi resolution, but on the high resolution maps, you may need to give your coastline a width of around 4 or 5 pixels.
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