Is there a map or site which can show airline routes on a map for most, if not all, airlines? I often see one for a single airline. Here it is for LAN Ecuador for example but I would like to see all airlines overlayed in order to plan an efficient multi-destination itinerary.
You may be interested in OpenFlights.org. There's a great blog post on it here:
and that was several years ago, it's come in in leaps and bounds since.
It doesn't quite describe what you're after (as far as I know) but it's pretty powerful in seeing which routes go from which airport.
Eg, type in MEL, select Melbourne Airport.
Click second icon to see all routes from this airport.
136 routes ex-Melbourne, all displayed on the same map.