[Imp]

Apart from doing the far left of the map its not much of an issue if you only have one monitor.
1)Open map editor & slide half of it off your screen to the left.
2)Open internet program with the map or google & resize it to fit in the other half of the screen.

Tip before generating the map have a quick zoom in & look at major long roads. If needs be adjust the angle slightly to match them.
Picture shows adjusted remembering while its a bit of a pita to do you can draw roads horizontally & vertically.
Can also consider when doing map if its for general play so rotating makes a more user friendly map.
i.e. Rotate town so edge runs roughly top to bottom & check it falls on one half of the map, as in edge of town is behind centre line so defenders can set up in all of it in a generated battle.