Blog · September 30, 2026
What PC and PT Mean on a Plat
PC is the point of curvature, where a straight tangent ends and the curve begins. PT is the point of tangency, where the curve ends and a straight tangent begins again. They are the hinges of the curve. They are not lot corners unless the plat also makes them corners.
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Entering and leaving the curve
Walk a straight road that starts to bend. The station where the bend becomes a circular curve is the PC. Walk until the road is straight again. That station is the PT. Between them the centerline is an arc with a radius and a delta. Outside them the centerline is tangent, meaning it just touches the circle and does not cross it at an angle. Subdivision plats use the same letters on right-of-way lines and sometimes on lot lines. A lot corner can fall at a PC, or it can fall partway along the arc, or it can fall on the tangent beyond the PT. The lot table tells you which. Assuming every front corner on a curved street is a PC will shorten or lengthen the frontage.
Related letters you will see beside them
PI is the point of intersection, where the two tangents would meet if they were extended. It often sits off the pavement, and it is a construction point, not a property corner. PCC is a point of compound curvature, where one curve meets a tighter or flatter curve without a straight piece between. PRC is a point of reverse curvature, where the bend flips the other way. If the plat labels only PC and PT, do not invent a compound curve. If it labels PCC, do not smooth it into one radius. Each letter is a change in the geometry. The curve table should give data for each piece. Copy the row that matches the segment you are reading, not the longest row on the sheet.
Monuments and the letters
Sometimes a plat calls for a monument at the PC or PT, and sometimes the monument is an offset iron on the right-of-way line. The letter is the geometry point. The symbol is the monument. They coincide only when the plat says they do. County GIS rarely plots PC and PT. It may show a curved parcel edge as a spline that looks close enough at neighborhood scale and is useless for a driveway permit. Platbookmapper links to that view and does not label curve points. Do not hunt a PI in the intersection with a shovel. The PI may fall in the travel lane, and digging there is not surveying. A surveyor stakes a PC from the plat data and the controlling monuments, not from a phone azimuth.
What to do next
- Mark PC where the straight line becomes the curve, and PT where it becomes straight again.
- Keep PI, PCC, and PRC as different events.
- Match each lot front to the segment it actually sits on.
- Do not treat a curve letter as a monument unless a monument is symbolized there.
The mix-up to avoid
Putting a lot corner on the PC because the street looks curved nearby. The front corner might be a distance along the arc from the PC. That distance is in the dimension, and skipping it slides the lot.
Questions people ask
Is the PC always the start when I travel north?
It is the start of the curve in the direction the course is written. If you read the deed backward, you meet the PT first. Follow the course order on the plat, not your commute.
Do building setbacks start at the PC?
Setbacks follow the plat and the zoning note, usually measured from the right-of-way line or the property line, not from the letters PC and PT. A curve changes how frontage is measured. It does not rewrite the setback note.
Find the county map
The county GIS map is the practical place to start. Find it from the Platbookmapper directory, then treat the recorded plat and deed as the documents behind the picture.
Not a survey. County GIS and tax parcel maps are assessment and planning layers. They are not a substitute for a recorded plat, deed, or licensed survey.