Assuming that others find it as irritating as I do when wilderness map progress is lost (I know there's probably a good reason for it, but that doesn't stop it being irritating), I have a suggestion. The Explorer Locations already found in an area are tracked by the game, and it is possible to flag an area's map as being fully visible (e.g. The Marketplace); so when a character has found all of the Explorer Locations in an area then the game could flag that character as being able to view the entire map for that area (i.e. the character has explored the place enough that they know it inside-out).
Admittedly, until all of the Explorer Locations are found the irritating disappearance of map progress will still occur, but that means being able to view the entire map is a decent incentive for tracking down the Explorer Locations (rather than the small amount of xp currently given for finding them all).
Am I missing something or does this appear workable?
<braces self for ridicule>