This is a "manual install" type of mod. You will likely need to move files into your game's data/maps or models folders. It may conflict with other "Total Conversion" mods that also modify the Little Haiti map files ( haiti.ipl or haiti.ide ). Safety Warning
As with any community-created .7z file from third-party sites:
It is generally a map or texture enhancement mod. The "plumping" part of the name usually refers to "filling out" the game world—adding more objects, vegetation, or structural detail to the Little Haiti area to make it look more modern or dense.
Based on the context of similar file names in modding archives, What is it?
Save a copy of your original game folder. Modding GTA files can easily cause the game to crash on startup if a file is misplaced.