The most common type of analysis I’m asked to do for my clients is a buildout. Buildouts are usually done in the context of a municipality’s comprehensive plan or zoning update. After assembling and examining a complete set of resource maps, my clients often request an analysis of how these resources interact, and where potential conflicts might occur. One way to accomplish this is through a buildout analysis.
In my 8 years working as a planner I’ve performed buildout analyses for over 25 towns and villages, often with multiple iterations per town. There are many websites outlining the process in general terms, but few get into the nitty-gritty tedious details neccessary to perform an accurate buildout. Most of those details I’ve learned through trial and error. One purpose of this series of posts is to share some of those details with others so they might avoid the pitfalls I ran into. If I’ve learned anything through my work with GIS it is that there is never just one way to do something. That being said, another purpose of this series is to encourage others to share thier experiences, and make suggestions about alternative methods of performing the many GIS operations required for a buildout.
Explaining the many steps involved in a buildout analysis in as much detail as I want to will require more than one post. So, I’ll start with an initial overview of the process and an outline of my plans for future posts which will include more of the nitty-gritty details.
Brief Description of a Buildout
A buildout analysis is an exercise designed to estimate the amount of development that can occur if all developable land within a defined area is developed according to a municipality’s land use regulations. The buildout analysis applies current land use regulations and typically considers environmental constraints that can limit development in certain areas. It then calculates the total residential density allowed at full buildout of the area. The defined area can be a single parcel being contemplated for subdivision, a neighborhood, an entire town or village, or a larger region encompasing more than one municipality. For this series of articles I will focus on buildouts performed for a single municipality, typically a rural town or village.
It is important to point out that these buildouts do not predict when full buildout will occur, at what rate it will occur, or where it will occur first. It only predicts the possible end result. There are some models that attempt to predict these characteristics, but my experience is that these models are wildly innacurate, especially when used for the small towns and rural areas I work with.
The Steps Involved
The general process followed to calculate full buildout conditions is:
- Identify areas that already have residential development and therefore would not allow new development
- Identify properties subject to conservation easements, or are owned by government entities not likely to allow development
- Identify areas in the town having environmental constraints that would not support new residential development
- Calculate the amount of new residential development allowed by the current land use regulations in the remaining develpable areas of the Town.
In essence, the analysis calculates the total land base of the town, subtracts all lands having environmental constraints and completely built areas, and then applies the various development rules to calculate the number of allowable new residences. For purposes of the analyses included in these posts, the buildouts will assume that all new development will be single-family homes.
It is important to note that the results of all of these calculations are only estimates. The GIS layers used are not exact replicas of what is actually found in the real world, only representations of what is there. The processing of the data also introduces a certain amount of error, and can add to the inaccuracy of the data. The only way to get an accurate count of allowed residential uses on a particular property is to do an on-site survey of existing conditions.
Outline of future posts
The following list outlines the specific steps involved in performing a buildout. I plan to describe these steps in much greater detail in future posts.
- Assemble the GIS
- Clean the data, add and populate appropriate fields
- Identify existing residential land uses
- Combine the zoning layer with the parcel layer
- Identify parcels that are currently fully built
- Combine the environmental constraints layers with the parcel layer
- Identify remaining buildable area within developable parcels
- Perform the buildout calculations on the remaining buildable area
- Report the results