So I was checking out the UV map to see if I could discover anything new and whilst most things have been covered and disclosed I noticed a lot of red triangles on the map, keyed as 'safe house' I went around looking at each of them to see if there was anything interesting about them. While there are a few in Los Santos that I missed (there are quite a lot of them). I managed to get around quite a few across the whole map. There isn't really much to them, the most interesting thing I noticed is that they all have a garage. Some don't interact but some of them do open.

Now I know this isn't any major discovery, it may have even been discussed before. But the point I bring up is why are they marked on the 'Secret' map and why are there so many of them?