Mapping without Seeing

[Gidde]

Step 4. Rivers.
Rivers are a lot easier than mountains; they're relatively simple shapes, and they follow some basic rules pretty darn consistently. Look at your inspiration map to see if the rivers are hairline, tapered, or outlined; that's all I take from the inspiration map. Most times I ignore the rivers on the inspiration map entirely, even, and just go with my own tapered rivers.

Look at your budding map. You have a coastline and mountain range(s), which gives you a rough idea of the contour of the land (high at the mountains and low at the coastline). Now draw in your rivers, keeping in mind the following rules: Rivers are really skinny when they start, get fatter the more tributaries dump into them, and end at a body of water (usually the ocean). Rivers are one way: high to low. As they go from high to low, they join up. They don't ever split (unless it's a delta or alluvial fan – both of which have great wikipedia entries). Deltas and alluvial fans are VERY rare. In mountains/hills, rivers tend to be relatively straighter, and grow more and more sinuous (and wider, usually) the flatter the land gets.

Got your rivers? Next is hills.