Site Plan Generators: What They Actually Produce

"Enter your address, get a site plan" is an appealing promise, and the tools making it are real and improving. It is worth understanding exactly what they do and where the line sits, because the gap between what these tools output and what a permit reviewer needs is specific and knowable.

What a generator is actually doing

Strip the interface away and almost every automatic generator runs the same three steps:

1. Geocode the address to a point on the map.
2. Pull the parcel polygon for that point from a public source: the county assessor's GIS layer, a state parcel service, or an aggregator that resells them.
3. Trace the structures from aerial or satellite imagery, increasingly with a model doing the outlining rather than a person.

The output is a tidy top-down drawing of your lot with the house on it. Nothing in those three steps involves your recorded plat, your zoning table, or a measurement. That is not a criticism of the tools; it is a description of the inputs they have.

Where the accuracy actually breaks

The interesting problem is not image quality. It is that a parcel polygon is not a boundary determination.

County GIS parcel layers are built for assessment and reference. They are assembled from deed and plat records fitted onto a base map, and counties publish them with explicit disclaimers saying so: the standard language is that the layer is for informational purposes and is not a survey. Positional accuracy varies enormously between counties and within them, and being off by a few feet is routine.

A few feet is fine for showing which lot is yours. It is not fine when the question is whether your shed is 5 feet from the line or 3, because that is exactly the size of the error. Setbacks are measured at the same magnitude as the data's uncertainty, which is why the last step of drawing a residential site plan is reconciling the GIS outline against the dimensions written on your recorded plat, and why that step cannot be skipped.

Aerial tracing has its own quieter version of the same problem. Imagery is taken at an angle, so roof edges do not sit above wall lines, and a traced building footprint is generally the roof rather than the walls. On a structure near a boundary the overhang can be the difference between compliant and not.

What is missing from generator output

Set the generated drawing next to what a reviewer checks and the gaps line up neatly. The third column is the part nobody advertises: what it actually takes to close each gap.

Read down that third column and the shape of the problem is clear: the generator supplies the picture, and every item a reviewer actually reads has to be added afterwards from documents the generator never opened.

The easement row is the one that costs money. Utility and drainage easements are recorded on your subdivision plat and are absent from the parcel geometry a generator reads, so a generated plan cannot show them and a homeowner trusting it has no way to know they exist. It is among the most common reasons a residential plan comes back, and it is the correction that forces a redesign rather than a redraw.

So will a building department accept one?

As submitted, generally no, and not because it was generated. Departments do not ask how a drawing was made. They ask whether it shows the required elements to a stated scale, and a raw generated base map does not: no project, no dimensions, no setback numbers, no easements.

The distinction worth holding onto is automation versus source. Building a residential site plan from county GIS and satellite imagery is the normal professional method for non-certified plans, and it is how ours are drawn. What makes the result permit-ready is not a different data source, it is everything done on top of it.

That work, in order: the traced parcel outline is checked against the bearings and distances written on your recorded plat and corrected where they disagree, which they usually do by a few feet; the roof outlines from the aerial are pulled back to wall lines, because imagery is shot at an angle and an overhang on a structure near a boundary is the difference between compliant and not; every easement on the plat is plotted; the project is placed and dimensioned; each setback is measured to the nearest projecting point and written as a number; and the stated scale is verified across the whole sheet rather than trusted from the software.

That reconciliation is the job. A generator does the first 20 minutes of it, and the remaining hours are where a plan either survives review or comes back. Across everything we deliver, 98% clear review with no correction notice at all, and revisions stay free until your building department accepts the drawing.

A small number of checklists ask for a "certified" or "stamped" drawing. That is a different document, produced by a licensed surveyor, and most small residential projects do not need one. Site plan vs plot plan vs survey covers how to tell which one your checklist is asking for.

Where generators are genuinely useful

A real list, not a dismissal:

• Sanity-checking your lot's shape and orientation before you start drawing anything.
• Deciding roughly where a project can go, early, when you are still choosing between the side yard and the back.
• Getting a base to trace over. Print the generated view and use it as an underlay, then add the dimensions from your plat.
• Talking to a contractor or a neighbor about placement without meeting on site.

What none of that produces is a submittable drawing. If you are using a generated base as a starting point, the blank site plan template gives you a permit-formatted sheet to transfer it onto, and the six-step walkthrough covers finding the boundary numbers the generator could not.

The three honest routes

Most small residential projects sit in rows two or three. A permit-ready site plan is drawn from county GIS records and satellite imagery reconciled against your plat, with setbacks dimensioned and easements of record included, and revisions are free until your building department accepts it. Across everything we deliver, 98% clear review with no correction notice.

For a fuller comparison of the drawing tools themselves, including the editors marketed as site plan creators and makers, see site plan software. For what happens once the drawing is submitted, see site plan review.