Isometric rendering and picking?
I've been looking for a formula to plot (world->screen) and mouse pick (world->screen) isometric tiles in a non-diamond-shaped world. What's the usual/correct way to do this?
I think you may be confusing some terms. Theme Hospital is diamond shaped from what I can tell. That's the shape of the tiles, not the entire world. You can shape the entire would however you like. The shape of the world would be the same as the shape of the tiles if the world was square (meaning equal width and height), but you don't need to make it that way.
You can use the algorithms described for this question. It's just an artistic style that will make it look like Theme hospital or Poxnora.