Blog · September 30, 2026
What Is a Radial Lot Line?
A radial lot line is a side line that, if extended, would hit the radius point of the curve it leaves. It meets the curved front at a right angle to the tangent. It is a design choice the plat has to show. Not every side line on a curved street is radial.
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Pointing at the center
On a cul-de-sac or a curving road, a surveyor can draw side lines that all point at the center of the curve. Those are radial. At the front corner, the side line is perpendicular to the street tangent, which keeps lot fronts from meeting the street at a sharp skew. The plat may say side lines are radial, or it may show a radial bearing on each line, or it may dimension an angle that is not 90 degrees and therefore is not radial. The picture at a glance is a fan. The proof is the bearing. A fan that looks radial and is actually a set of parallel side lines is a common misread, because at a gentle curve the two designs look alike on a small sheet.
What it does to frontage and width
Frontage along the arc and width at the setback are different numbers on a radial lot. The lot gets wider as you walk away from the center on an outside curve, and narrower on an inside curve. A building envelope drawn with parallel lines on a radial lot will not match the plat. Zoning rules that measure width at the building line, not at the curb, exist because of this fan. Read the width where the note says to measure it. Do not measure the arc at the curb with a wheel and call it the lot width. A wheel is not a survey, and the curb is not always the property line. The right-of-way line may sit behind the curb, and the lot line is that line or another line the plat names.
Nonradial neighbors
Some plats use nonradial side lines on purpose, so a lot stays more rectangular or so a line hits an existing monument. Those lines meet the curve at a skew. The front corner is still a point on the curve, but the included angle is not a right angle. If you assume radial when the bearing says otherwise, you swing the rear corner by feet over a deep lot. The error grows with depth. County GIS almost never encodes radial versus nonradial. The parcel edge is a general shape. Platbookmapper links to it for finding the account. The recorded plat’s bearings are the authority for whether the side line is radial. If you need the line staked, a surveyor uses those bearings. You do not swing a string from a guessed center point in the middle of the bulb.
What to do next
- Read whether the plat says the side lines are radial.
- Check one side-line bearing against the radius bearing.
- Measure width where the plat or the zoning note says, often not at the curb.
- Do not project a radial line to a center you guessed from an aerial.
The mix-up to avoid
Fanning every side lot line to the middle of the cul-de-sac because the lots look like slices. If the bearings are not radial, the slices are skewed on purpose, and the guessed center pulls every rear corner off the plat.
Questions people ask
Does radial mean the lot line is curved?
No. The front is curved. The radial side line is straight, aimed at the curve’s center. A curved side line would be a different call and would have its own radius.
Is the rear line radial too?
Not as a class. The rear line is whatever the plat draws, often a chord, another curve, or a line between two rear corners. Each rear corner is the end of a side line. The rear line joins those ends and needs its own bearings.
Find the county map
Search the county on the Platbookmapper home page. The directory links to the official parcel viewer. It does not draw the lots, and the line on the screen is an assessment map, not a survey.
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.