[Routing] handle zooming far out

[marcus.wolschon at googlemail.com]

Hello everyone.

I wonder, how are all the other navigation-apps
who's developers are on this list handle the user
zooming out to show a large city, state, country
or even continent in interactive rendering?

Do you switch to pre-computed tiles at some point?
Keep a simplified vector-map?
Do not allow the user to zoom out that far?
...

Marcus