Every once in a while, when we chat with an expert in zoning, we love asking the question: what do you think is the most common error made when gathering zoning information?
So far, the consensus seems to be: understanding the overlays.
Every jurisdiction often has multiple layers of overlay that modify the base zoning.
Overlays go by different names depending on the jurisdiction (in Portland, we have Overlay Zones, but also Pattern Areas and Plan Districts; in Austin, there are Combining Districts and Specific Area Regulations). But they are essentially delineated areas of additional regulations that modify or override the underlying zoning districts.
Sometimes they're part of the zoning code. Sometimes they're outside of the zoning code, but in another part of the city codes or ordinances (like in San Diego, with their recent CCHSA ordinances).
You could be forgiven for thinking that to acquire zoning information, you need to just look up the zoning designation and then find the regulations that are attached to that designation.
Often, much of the work involves finding all of the other overlapping areas which modify the development regulations, and then understanding if and how those areas modify your base zoning designation.
For example, in Portland, here is a map of the base zones. There are 28 base zone designations in total.
And here is a map of the Pattern Areas. There are 5 Pattern Areas. These broad districts modify the base zones underneath.
And here is a map of the Overlays. There are 20 Overlay Zone designations, but a site may be afflicted by more than one overlay. These Overlay Zones modify or override the base zones, which had already been modified by the Pattern Areas.
On top of that, there are Plan Districts. There are 32 Plan Districts, and thankfully, they do not overlap, so no site belongs to more than one Plan District. These Districts override the Overlay Zones, which override the Base Zones, which are modified by the Pattern Areas.
And here is a map image of the Overlays and Plan Districts combined; in sum total, almost exactly half of the sites in Portland are modified by an Overlay Zone, a Plan District, or both.
This complexity is part of the reason why we've created the Guides to Zoning. We wanted to make sure that the process for acquiring zoning information was well understood--for the benefit of any person who wants to understand the regulations that define our city.
Check out those Guides to Zoning here: How do I find my zoning? | UrbanForm
We'll continue to add to them throughout the coming year :)