I was puzzled by this too, but I think it's an artifact of the way the map is done. I live in one of those $1800+ zones and I couldn't find a 1BR on the market

I was puzzled by this too, but I think it's an artifact of the way the map is done. I live in one of those $1800+ zones and I couldn't find a 1BR on the market for under $3000 last summer. My guess would be that mean per bedroom would be $2500 in that area (including studios and economy of scale for larger places), but I bet it gets lumped in with $1800+.