A region like Great Britain
This is a map made for a request on an RPing forum. The brief was pretty simple - a region like Great Britain, and an appearance like some maps I'd made previously. As is the norm for regional maps by me, it's GRASS work. Squares are 100 km across, scale is thus 1 pixel = 500 m. The highest mountains are ~ 1500 metres. (For those caring about projections, I actually used British National Grid, which is a transverse Mercator projection).
A few notes:
The island shape is constrained by making a coastline, then taking the square of distance outside it. (I actually used the coast of Great Britain). This is then divided down appropriately and subtracted from randomly-generated fractal terrain. In this case the constraining was "weak", mainly just ensuring one gets an island even when the original generated terrain has land along the borders.
I took the cube of the random terrain; this creates the divide between smooth lowlands and rugged uplands.
I tried some erosion. Having run the rivers model (r.watershed), I took the square root of the discharge, blurred that, and converted it to a percentage of height to remove from the DEM. I really want a better way to do erosion. Maybe figure out how to transfer data between GRASS and Wilbur.
Depression fill gave bugs on this elevation model, and I didn't feel like doing lakes, so I might have some uphill-flowing rivers.
It's not super-similar to Britain, but it's the right size and I think I've got a good balance between lowlands and uplands. Erosion is the main deficiency. (And, arguably, that unlike Wilbur's terrain generators GRASS's doesn't make mountains with ridges.)