Review the steps to run the Buildable area analysis on all parcels on a project and read more about each available setting.
Run Buildable area analysis on all parcels
Add parcels to the project first before running the Buildable area analysis.
In the left sidebar on the project, click Buildable Area to open the Project Buildable Area Analysis form.
You can also run the Buildable Area Analysis on just a subset of parcels on a larger project, if you prefer.
Buildable area analysis form
The Buildable area analysis form has one or more tabs of settings, depending on the region you are analyzing and if you subscribe to Predictive flood mapping.
- General Settings: Set internal parcel boundary setbacks and ensure that areas are only marked as 'buildable' if they are practical to build on.
- Layer Settings: configure key exclusion and intersection settings and setbacks
When the Buildable area analysis form first opens, its organizational sections are initially collapsed.
Click a layer category to expand the full settings.
General Settings
Use these settings to help get a more realistic final calculated buildable acreage / constraint map. Set an internal setback for parcel boundaries or input criteria to help filter out small and narrow, isolated sections that are too small for practical siting purposes.
For example:
If a 1-acre section of a parcel was not in a hazard or a setback, then it would technically be marked as being 'buildable', but in practice, if that buildable area is not connected to a larger buildable section, it shouldn't count towards the total buildable acreage.
Minimum Buildable Area
Input the minimum contiguous buildable area size allowed.
Depending on the size of the parcels on the project, it's best to set this much lower than the total desired acreage. The goal is to eliminate sections that are obviously too small, while avoiding excessive automation that removes sections which are still useable.
Start with 2-3 acres for projects with smaller parcels; for projects with larger parcels, try starting with 5-10 acres.
Sliver Removal
Long skinny sections of buildable area (slivers) are often not a good fit for siting projects. Remove these slivers from the buildable area to get a more accurate final buildable acreage calculation.
Choose sliver removal setting level:
- Regular – uses 40 m. in diameter circle to check for sliver width; anywhere that the circle doesn't fit will be marked as too small to be buildable)
- Aggressive – uses 100 m. in diameter circle to check for sliver width; anywhere that the circle doesn't fit will be marked as too small to be buildable)
Parcel Boundary Setback
Apply an optional internal setback from the parcel boundary line to ensure that you're not building right up to the edge of a property (follow local municipal guidelines for exact setback distances).
Input Parcel Setback (internal): Commonly about 25-50 ft in most of the U.S.
Slope
Automatically identify slope percent values in an area and remove areas with too steep of a slope from the buildable area. Includes the option to separately analyze slope percent according to the slope aspect.
- Toggle on the Slope setting.
- Select All Aspects or Per Aspect.
When All Aspects is selected, the Max Slope (%) field that appears applies to all slope aspects. To analyze slope aspects separately, select Per Aspect (N, S, E, W).
- Input a Max Slope percent. Read about Max values for information about how the Buildable Area Analysis evaluates Max Slope.
When using Per Aspect, input Max Slope % for any/all slope aspects you wish to include in the analysis. Leaving one or more Max Slope (%) field blank when using Per Aspect means those aspects are not analyzed and cannot affect the buildable area or create an Overlay Only drawing.
Degree ranges used for each slope aspect
- Northern: 315 to 45 degrees
- Eastern: 45 to 135 degrees
- Southern: 135 to 225 degrees
- Western: 225 to 315 degrees
- Choose an Analysis type (e.g. Exclusion)
- (Optional) Input a High Slope Setback value to apply an additional buffer around the high slope areas (many developers leave this off at this stage of siting if you're unsure).
Advanced Slope Settings
Input more than one slope percent value for additional visibility into slope intervals on the constraint map.
In the Max Slope (%) field, add two or more space-separated slope levels to see additional shading on the map. e.g: "5 10 15"
In this example:
Max Slope is 15% and the Analysis type is Exclusion. Any areas with slopes greater than 15% are Exclusions and those areas will not be buildable. Any areas with slopes less than 15% will be included in the buildable area calculations and marked as buildable.
The example includes the intervals 5-10% and 10-15%. Distinct shadings for the 5-10% slope areas and 10-15% slope areas appear on the Constraint Map, in addition to the 15%+ shading.
The lowest slope interval, < 5%, is implied by the value '5, 10, 15'. By default, the lowest slope interval is transparent. To see shading on the map for the lowest interval, select the Include lowest slope in output drawing checkbox.
Adding multiple slope levels, particularly when using Per Aspect, significantly increases the size of a project's constraint maps. Therefore, we recommend avoiding these advanced settings when running analysis on a larger project.
Minimums and maximums
Some layers in the Buildable area analysis are a special type where the layer is made up of a grid where each cell in the grid has a numerical value assigned to it. These layers are called rasters. The numerical values in the cells represent characteristics such as bedrock depth, tree coverage %, or flood depth.
When evaluating a raster layer in the Buildable Area Analysis, there is either a Min (minimum) or (Max) maximum field where you can provide a threshold value.
The Slope layer uses a Max value setting as well.
Taking Trees with Exclusion analysis as an example, if you specify 50 as the Max tree cover (%), this means areas with over 50% tree cover are Exclusions, so only areas with 50% or less tree coverage are marked a buildable.
Taking Bedrock Depth with Exclusion analysis as an example, if you specify 2 m as the Min bedrock depth, this means areas with under 2 m bedrock depth are Exclusions, so only areas with 2m or more are marked as buildable.
This direction of logic applies to Intersection and Overlay Only analysis type as well. Imagine you are working on a project where you are building a structure that must be anchored to bedrock near the surface. If you specify 2 m as the Min bedrock depth with Intersection Analysis, then areas with less than 2 m (200 cm) bedrock depth are Intersections and will be marked as buildable (assuming no Exclusion areas are also present in the same location). Note how areas with Unknown bedrock depth are not marked as buildable.
Run the analysis
Once the form is configured as desired, click Run at the bottom of the form to run the analysis.
In the background, each of the enabled hazards is analyzed and any setbacks applied.
Track the progress of the buildable area analysis in the notifications on the project window:
There is no need to keep the project (or task pop-ups) up while you're waiting for the analysis to finish processing. This task runs in the background even if you close the project window or task pop-ups.
On the project map, the parcel constraint maps will load in as they complete.