I just realised in my previous message, I didn't talk about what I want to use this map for.

I actually want the ability to make many maps. That's one reason I've got my own software in the pipeline. Maybe we want an Empire-wide military report -- I could render out a copy of the full map, with territories coloured by ownership and disputed borders highlighted. Or maybe we want something that shows the locations of all fortifications in one region: render something a bit more zoomed in, with icons for the forts.

My largest Empire-wide maps will be printed at up to A1 size, but I imagine any regional ones I do would be smaller.

Thus, I need a height map that'll work as a background for anything from the whole Empire-wide map to a map of an individual territory to a region within a territory. However, since the height map is just a background feature for many of the maps, it doesn't have to be super detailed. I'd be happy enough if it could convey where was mountain vs hills vs plains in the zoomed in maps.