A world document's own country as a greyscale heightmap.

Draws the open country a world document generates (its worldgen block: seed, knobs, regions with their own relief, a ridge) as one greyscale PNG, row 0 north, so a world built with world_apply can be looked at before anyone walks it. area {w, h} makes a block of chunks from chunk (i, j) (w times h at most 25); range [lo, hi] fixes the grey scale in world units. The answer carries the height range, the grey scale used (greyFrom, greyTo, unitsPerGrey) and the name of the country each chunk sits in. A world with no worldgen block is bounded and is refused by name; set_worldgen opens it onto boundless country. Costs 1 unit.