Not to be confused with the AH Challenge in which a POD question is posed (e.g. “Challenge: How can we get a Muslim CSA by 1734 ?”). Instead, Map Challenges are more of the 'what happened here' type, in which a map is posted and the poster asks viewers to surmise how the world got to that stage.
Often, the original poster doesn't quite know themselves and is hunting for ideas from the viewers. Sometimes this can still provoke useful discussion and eventually a collaborative timeline. For example, an older Map Challenge by Hermanubis, seen in the thread Medieval Map, created the successful ATL Dark Ages Map TL, written by Midgard.
However, if the original poster comes across as lazy or reacts indignantly when people fail to justify the political prejudices that informed the map, things get ugly. Gladi created a put-down for the lazier Map Challenges : “How did we get this map? Easy, you drew some lines on a blank map and coloured it in”.
Map and Flag Challenges are also distinct from Map and Flag Contests, which are just that. While the M&P Challenges are a kind of one-off logic game for one's imagination, M&P contests involve the creation of alternate history maps and flags by multiple members for contest purposes. (Though it also needs to be said that one currently running contest is named the 'Weekly Flag Challenge', with no intended relation to the usual map and flag challenges.)
Map and Flag Contests - Contests involving making alternate history maps and flags within the framework of differently themed individual rounds, and subsequent voting for the winner of each contest round.