Updates:
I know, bit of an odd one, but someone brought this up to me last year as a possible mod and I realized I liked the idea as the lot outlines on the maps ruin the aesthetic of the EA and override maps. Fast forward to now, and thanks to Pancake who figured out which file I needed, the mod is finally here!
Right now there are two versions (check second image for comparison):
Removed: Completely removes the lot outline on the maps.
Thinner: Makes the lot outline on maps thinner.
Only choose one version! If you have trouble finding the lots with the Removed version, I recommend getting the Thinner version instead. Before anyone asks, I can't make the outline any thinner than I already did. Also, this mod does not currently affect build mode lot outlines, it only changes the map outlines. I will try investigating if that one can be removed as well but no promises. Edit: TwistedMexi has confirmed it’s not possible to remove the build outline, sorry!
This is a UI mod but currently has no conflicts out there, so will work with map overrides, TOOL, More Traits in CAS, etc. Since it is a UI mod please be aware that it might need an update every patch, but from current testing this seems to be a rare file where EA doesn't touch it much.