Canvas wouldn't graphically scale as nicely. You could argue that SVG would be more appropriate, but this solution works on the old Android 2 browser whereas SVG doesn't.
Could probably ensure it fits in the window nicely though, with zooming etc. Seeing only the North-West of London on screen without scrolling is not as useful. I'd imagine it's damn hard to use on a laptop without two direction scrolling. Functional over pretty, I vote :)