Ahh, yes. It's 3x256 wide and 4x256 tall. But I don't see any way to do big city with little tiles.
This is the widest avenue I'm planning. I'll also be making street tiles that are just 1x256 wide, and possibly a tile with the rail and streets that are one lane wide, making the whole thing 2x256 wide.
Also, what you see here will eventually be two tiles, that can be matched together or not if they're on the edge of the map (the rail stop can be split in two vertically).
But I am planning city blocks to be about 4x256 squares, and if we're talking about tall buildings, that means that each block will probably be one tile, though I've thought of a few minor exceptions.