Prop map perftweaks

These are O(n) to O(1) perf fixes in the way that PropMap is used. This bumps up some speed in markers and clustering markers. I wanted to tweak PropMap before I go ahead replace the clustering logic.
If we start seeing issues then we should turn this on, otherwise this is an O(N) on a lot of clustering. It should maybe be done at random or much less often. Currently it is disabled.