If they're on the map but not showing in Basecamp check Options, Activity profile, Map features to be displayed and check the relevant parts are checked.
I'm very slow at this - I do not see any "options". In preferences I can get a display choice and there I have a hide map details choice. But I can't figure out what that means - am I hiding what I check or don't check? Icons show up on very heavy zoom in, like 200 ft, but I would like them at a much larger area, say 5 miles.
It's under Utilities in Windows version, not sure about the Mac.
As for the zoom issue, that's a different problem and AFAIK you can't alter the zoom level at which POIs appear/disappear but you can affect whether they appear or not by setting the map detail level. However IMO having POIs at the 5 mile level wouldn't help much as it would just be a massive blob of POIs, it's often difficult enough to make them out individually when the zoom is at 1 mile.
... In preferences I can get a display choice and there I have a hide map details choice. But I can't figure out what that means - am I hiding what I check or don't check? ...
If you check them they show up, so you are hiding what you DON'T check.
That of course is exactly opposite of the way one would think it worked under a selection entitled "HIDE map features"
