That helps a lot, thank you! A district is a connected group of hexes. With the other districts you have drawn, there is no way to create a connected group of hexes containing all remaining colored ones
Connected hexes meaning "connected _occupied_ hexes"? It certainly seems to let you select empty hexes. Is it that the "size" of a district is based on area, rather than population (as in the real world)?
No, that's not it. Is it that some empty hexes (not just outside the map, but inside as well) are mysteriously not allowed?