That would be everywhere. Even the most boring border in the world is political: https://en.m.wikipedia.org/wiki/List_of_areas_disputed_by_Ca...
US-Canadian border is definitely one of the more intense borders I crossed. And some of the horror stories I heard (e.g. Peter Watts) sound pretty bad. It might be the most boring US border though.
Really boring borders can be found in EU/Schengen where you drive by a sign announcing a different country and that's it. There are even more boring (and interesting at the same time) borders: https://en.wikipedia.org/wiki/Baarle-Nassau#/media/File:Baar...
That said, content moderation tends to employ people who are experts in the region, with academic backgrounds in history, politics and such. They're likely coming in with strong opinions. Cartography may different.
^Safety, or whatever name they use internally.