This is an unpopulated neighbourhood, or what the game calls a Terrain, complete with roads and ready for you to add Lots and Sims.
To use in your game - unzip the file into your folder
My Documents\EA Games\The Sims 2\SC4Terrains (which is probably in your C:\ drive, rather than in the usual Sims 2 directory - if you can't find it search your computer for SC4Terrains.)
and then in Sims2 use it to make a Custom Neighbourhood. Instructions