Computer generated terrain usually begins with a base of random noise, or perhaps a fractal. These look nice in small sections, but are unconvincing for a continent: noise has none of the major features it should, like mountain ranges, and fractals are nothing but feature -- they're too regular. Here's a method for generating continent-level trerrain using distortion fields.
Elaborations have indeed produced better results. Simply having water flow over a surface was not terribly hard to implement, but each sophistication -- even within the limits of a cell-based, time-step-based system -- have paid off. Initially, I tried having water flow according to the landscape alone, without recomputing where water was pooling; adding it in allowed much longer rivers to develop, as well as lakes (the lakes were all I expected to gain). Adding even a very crude momentum mechanism -- to prevent immediate back-flow when water is evening out over an area -- eliminated a strange checkerboard artifact.
Here I present a surprisingly easy way to fill valleys in a rasterized elevation map, for the purpose of creating realistic rivers quickly.
This post is about a world-building tool I've been working on. The goal is to generate semi-realistic landscapes including rivers and other effects of erosion. The tool is a bit of code, written in R. At heart, it models a map in the form of a grid, where each cell has an altitude, forming a height map.