Would it be to hard to...?

[Geos]

Using location in Scenario Building is something very common. Many of these locations are areas that we could define for several purposes, like the [avoid] tag, or [time_area].
When defining areas, I found no good way of defining besides:
x=14-25
y=2-13
Which are always square like. If you want to make a better definition you have to define every location individually.
Maybe there would be a way to store that information in the map file, in the way of tags to the hexes, the same way the Player Starting Location works.
This way, from the map editor, the user could draw an area, adding the same tag to each hex selected, so that later it would be retrieved from the map as an array of locations, something like:
[avoid]
area=$MapArea.area1
[/avoid]
Areas could be coded with a symbol, to let know the parser that we are talking about an area, and with a number, to allow multiple areas in the map. Something like

Xx^yy %1,

What i don't know is if it is too hard to implement as I haven't taken a look at Wesnoth's source code. I definitely doubt I would have time to work on this, but if somebody considers it a good idea, I'm willing to help.

[AI]

Terrain masks are probably what you're looking for. It doesn't seem to be usable for every thing you want to do with it though. (if at all, it's mostly for changing terrain and fog and such)

[Geos]

Yes, terrain masks I have already use. It is just an idea, just in case somebody hadn't though of that, although, most likely, somebody had actually thought of that, but people just don't find time to develop every single thing.
Maybe it would be easier if a terrain_mask could be used as an input for a filter.