What makes PD-15’s gyrations different from many other upzoning cases is that there is no blueprint to follow. The Toll Brothers building in Oak Lawn largely fits within its MF-3 zoning. Sure, some complain whether MF-3 is appropriate for the area, but it’s there. Other projects have MF-2 and want to move beyond those controls. But PD-15 has none of that to act as starting point. The PD documents essentially state a total number of units in the PD that is derived by the number of units per acre. There’s also a bit on parking and interior street right of ways. But that’s pretty much it.
If you’re talking about traditional city zoning, there are categories for setbacks, density (units per acre and size of units), height, lot coverage, primary uses and any special standards (like a minimum lot size or proximity slopes). Proximity slopes protect neighboring buildings from being too close to radically taller structures by forcing them to literally step back from those neighbors (think of stair steps back).