While there is a vectorization tool in Xara, I wouldn't copy an outside map verbatim, rather I would completely redraw the map, buildings, street plan in your own digital line work, so that your map is now completely your own. Copyright law applies to existing maps, so don't make your map an exact copy of the one you reference - make it close to match your city, but not exactly match the map. Once your map is ready, you can draw shapes apply variated colors to each one to differentiate each sector as stated in my previous post. That's how I'd do it anyway.

GP