[Xinhuan]

The information for zone sizes and offsets from the continent parent map are basically available in the .dbc files you can extract using an MPQ extractor. GatherMate and Routes (which I wrote) uses these data.

Astrolabe's data doesn't come from the .dbc files though, it comes from pure observation and testing of values and then tweaking them ingame until they fit. HandyNotes (which i wrote too) uses Astrolabe.

You can take a look at LibMapData-1.0 on wowace, where we are setting up a new library containing just map data and some conversion and zone name localisation functions for general use that we intend to use for the GatherMate/Routes/etc addons. Instead of using mapFile names as unique map identifiers, it uses the unique zone IDs introduced with Wintergrasp (data also available in the .dbc files) for every zone in the game. This includes instances.

LibMapData-1.0 will be built to also handle phasing maps (there are a number of zones where the zone map is different based on the phase you are in) as well as dungeon levels. The coordinates used internally is being expanded from 8 digits to 10, but we may expand this to 15 digits (the max integer that can be saved with accuracy).

[P.S. I'm not trying to advocate any library or data over another. Just giving some options and sources of data.]