The short answer
A building footprint report shows the outline of each building on a property as seen from above, with its dimensions and ground-floor square footage. In insurance it is also called a property diagram, plot plan, plot map, site diagram or sketch diagram. PropDiagram produces one from a street address in about a minute. The building footprints are drawn and measured automatically from aerial imagery. Occasionally walls and dimensions may need to be tweaked for better accuracy, using the tools provided with every report.
- Pay on successper report or monthly subscription; no contract
- About 1 minutefrom address to finished diagram
- 140 million+building outlines on file
- Lower 48 + DCurban and rural addresses
What is a building footprint?
A building footprint is the outline of a building at ground level, viewed from directly above. The area inside the outline is the building's ground-floor square footage, often written as 1st-floor square footage.
| A footprint measures | A footprint does not measure |
|---|---|
| The shape of the building on the ground | Upper floors, mezzanines or basements |
| The length of each exterior wall | Roof area, pitch or roof facets |
| Ground-floor (1st floor) square footage | Interior, finished or rentable area |
| Where the building sits on the lot | Construction type, age or condition |
For a single-story building the footprint is the building's square footage. For a multi-story building it is one floor; in PropDiagram you tick Multi-Story and enter the upper floors, and the report shows 1st floor, 2nd floor and above, and the total.
How are building footprints made from aerial imagery?
- Imagery. Aircraft and satellites photograph the ground. The images are corrected so that a distance measured on the picture matches the distance on the ground.
- Detection. A computer vision model finds each roof in the image and traces its edges into a polygon with real-world coordinates. The result is a machine-detected building outline.
- Matching. PropDiagram keeps more than 140 million of these outlines for all of the lower 48 states and Washington, DC. When you enter an address it finds the property, and its tax parcel where county parcel maps are available, and selects the buildings that belong to it.
- Measurement. Each building is measured: the length and width of its best-fit rectangle, the length of every wall on an irregular building, and the footprint square footage.
- Drawing. The buildings are drawn to scale and numbered, with adjacent streets, a north arrow and a scale bar, and laid over an aerial photo so you can check them.
What is in a PropDiagram building footprint report?
On the diagram
- Numbered building outlines, to scale
- Dimensions on every building
- Lot lines with edge lengths*
- Adjacent streets, labeled
- Fuel tank and wood boiler icons you place
- Scale bar and north arrow
In the schedule
- Building number and the name you give it
- ACV, RCV or N/C for each building
- 1st-floor square footage
- Upper-floor square footage you enter
- Total for each building and for the property
- Lot size, acreage and building coverage*
In the PDF
- Property address and parcel ID*
- The building schedule
- An aerial view of the property
- A full-page diagram with the legend
- An accuracy note
* Lot sizes and boundaries when available
Done for you, or do it yourself?
You can measure a building on a free online map by clicking its corners. It works for one building. The work is in everything around it: every building on the lot, a drawing someone else can read, and a schedule that ties each building to the policy.
| Step | Measuring it yourself on a map | PropDiagram |
|---|---|---|
| Outline each building | Click every corner of every building | Drawn automatically; tweak a wall if needed |
| Dimensions and area | Read off each measurement and write it down | Measured automatically and printed on each building |
| A drawing for the file | Screenshot, or sketch by hand | Scaled diagram with north arrow and scale bar |
| Building schedule | Type it up | Numbered schedule with names, valuation basis and square footage |
| Lot lines and lot size* | Look up the county parcel map | Added automatically when available |
| Corrections | Start the measurement again | Move one wall, or redraw one building |
| Cost | Your time, every time | A low per-report cost, charged only when the report succeeds |
* Lot sizes and boundaries when available
How accurate is it, and what if a building is wrong?
Outlines detected from aerial imagery are typically within a few feet of the building. The usual causes of a difference are trees over the roof, shadows, wide roof overhangs, attached structures that were joined to or split from the main building, and buildings newer than the imagery.
That is why the report opens with the outlines on top of the aerial photo. If one is off you can:
- Adjust walls: move any wall in steps of 1 ft or 0.1 ft, or drag it.
- Add a building: click the corners of a building that is missing or newer than the photo, then type its size from your field measurement, for example 40 x 60.
- Remove a building: take off a neighbor's building, or clear them all and trace your own.
- Measure: draw a line between any two points to check a distance.
These tools are part of every report and cost nothing extra. A building you drew by hand is marked on the report so a reader knows.
Who uses building footprint reports?
Mostly property insurance professionals, because so much depends on knowing what is on a property and how big it is:
- Agents and brokers, to document what was insured and reduce errors and omissions exposure.
- Underwriters, to check square footage behind insurance to value and find buildings that are missing from the schedule.
- Loss control and risk management staff, to record the site, fuel tanks and distances between buildings without a second visit.
- Claims adjusters, to see what stood on the property before the loss.
Common questions
What is a building footprint?
A building footprint is the outline of a building at ground level as seen from above. Its area is the ground-floor (1st floor) square footage. It does not include upper floors, basements or roof overhang measured as roof area.
How are building footprints made from aerial imagery?
Computer vision models trace the edges of each roof in aerial or satellite images and convert them into polygons with real-world coordinates. PropDiagram keeps more than 140 million of these outlines for the lower 48 states and Washington, DC, and measures the ones at the address you enter.
How accurate is a building footprint from aerial imagery?
Typically within a few feet per wall. Trees, shadows, roof overhangs and attached structures can shift an outline, which is why PropDiagram shows it over the aerial photo and lets you move any wall in steps of 1 ft or 0.1 ft.
Is a building footprint report the same as a plot plan?
It is the insurance kind of plot plan: a scaled diagram of every building on the property with its dimensions and square footage, also called a plot map, site diagram or sketch diagram. It is not a surveyed plot plan of the kind filed for a building permit.
Is footprint square footage the same as total square footage?
No. Footprint square footage is one floor. For a multi-story building, tick Multi-Story and enter the 2nd floor and above; the PDF then shows 1st floor, upper floors and the total for each building.
Can I get a building footprint report for a rural property?
Yes. Rural addresses in the lower 48 states and Washington, DC are covered the same way as urban ones. Farm and rural properties with several outbuildings are a common use.
What does a building footprint report cost?
Pay per successful report or subscribe monthly with reports included; current rates are on the Pricing page. Editing and downloading again are free.
A PropDiagram report is a diagram and reference record. Measurements are approximate ground-footprint estimates from aerial-imagery-derived building outlines. A report is not an appraisal, survey, replacement cost estimate or insurance valuation; verify anything a decision depends on.