I am currently testing through my own scenarios and heightmaps. And I will upload them with the game itself so you can download the whole thing. Just unzip the file, doubleclick or make a shortcut to the openttd.exe and play.
This is a OpenTTD scenario I developed further from the first “Compass Cities” scenario. It has a lots of iron ore mines and forrests. Some farms and factories are there too. And a lot of oilwells.
Climate is temperate.
Scenario size is 256×256 squares.
This is a OpenTTD heightmap made in MS Paint. I used the mouse to draw with. Better with a penlike device, maybe…? Anyway, this is a great way to makes more complex terrain in scenarios.