Blog · September 30, 2026
How to Read a Curve Table
A curve table collects radius, delta, arc length, chord bearing, and chord length for each numbered curve on the plat. The number on the arc has to match the row. Mixing row 3 with curve 5 builds a different lot.
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The columns that usually appear
A typical row gives a curve number, a radius, a delta angle, an arc length, a chord bearing, and a chord length. Some tables add a tangent length, a radial bearing, or a direction left or right. The arc length is the distance along the curve and is the usual frontage if the lot line is that curve. The chord is the straight line between the same two ends. It is shorter than the arc and has a bearing so you can place the ends. Using the chord length as the frontage understates the arc. Using the arc length as if you could pull a tape straight across the chord will not close the figure. The radius is to the center, which may lie far outside the sheet. Delta is the central angle. All of those numbers belong to one curve number. The number in the balloon on the map is the only safe way to join them.
Match the row, then match the lot
Curve C4 may be the right-of-way centerline, C5 the right-of-way line, and C6 the lot line offset from it. They can share a delta and differ in radius by exactly the offset. If you assign the centerline row to the lot, the lot grows or shrinks by that offset along the whole front. Read the leader. On a busy cul-de-sac the leaders cross, and a scan makes it worse. Zoom the recorded image, or get a better copy, rather than picking the nearest row. If two curves share an end point, the PT of one may be the PC of the next. The table will use two numbers. Do not merge them because the line looks smooth.
A consistency check stays on paper
For a circular curve, the chord length, the radius, and delta are related, and so are arc length, radius, and delta. You can check a row for a typographical break. A small difference is rounding. A large one is a reason to look for an affidavit of correction or a revised sheet. It is not a reason to stake the version that fits your porch. County GIS does not carry the table. Measuring the drawn curve there gives a screen approximation. Platbookmapper does not reproduce curve tables, draw lot lines, or show zip codes. It links to the county assessment viewer. The table you want is on the recorded plat. A laser measure in the field is not a survey and will not reproduce delta.
What to do next
- Match the curve number on the map to the same number in the table.
- Copy radius, delta, arc, chord bearing, and chord length as one set.
- Keep centerline, right-of-way, and lot curves distinct.
- Use arc length for travel along the curve and the chord when the course is the straight connector.
The mix-up to avoid
Taking the chord length as the lot frontage. Buyers and fence builders like the shorter straight number. The frontage call along a curve is the arc, unless the deed clearly says chord.
Questions people ask
What if the table and the dimension on the arc disagree?
Note both numbers and look for a correction or a later plat. Do not average them. Averaging creates a third curve nobody recorded. A surveyor can tell you which figure the rest of the geometry supports.
Are all curves in the table circular?
Most lot plats use circular curves, which have one radius. A spiral or a compound curve needs different data. If the table has a single radius and a delta, read it as circular unless the sheet says otherwise.
Find the county map
Open Platbookmapper and pick the county that taxes the land. Use that viewer to get the parcel id, then match it to the recorded plat if you need the easements and lot numbers.
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.