Blog · September 30, 2026
What Is a Nontangent Curve?
A nontangent curve meets the previous course at an angle instead of gliding off a tangent. The plat has to give a radial bearing or a chord bearing so you can place it. Treating it as a simple tangent curve twists the lot.
Platbookmapper is an Amazon Associate. If you buy through an Amazon link on this page, we earn a commission. The link is a product, not the county map.
When the curve does not kiss the last line
On a tangent curve, the radius at the PC is perpendicular to the incoming straight course. You can leave the straight line and enter the curve without a kink in the direction. On a nontangent curve, that perpendicular relationship is broken on purpose. The incoming line and the curve meet at a corner in direction. Cul-de-sac returns, some lot fillets, and many descriptions written from coordinates come out nontangent. The clue on the sheet is a note that says nontangent, or a radial bearing that is not at right angles to the previous course, or a chord bearing that will not fit a tangent assumption. If you force a tangent construction, the end of the curve lands in the wrong place even though radius and arc length look familiar.
What data replaces the tangent assumption
You need a way to orient the radius. A radial bearing from the PC to the radius point does that. A chord bearing plus the chord length can do it if the rest of the data is consistent. Delta and radius still describe the shape of the slice. They do not, by themselves, say how the slice is rotated relative to the last course. So a table row with radius, delta, and arc length, and no chord bearing and no radial bearing, is incomplete for a nontangent curve. Note the gap instead of assuming the tangent case. Survey software will sometimes assume tangency when the field is blank. That assumption is the software’s, and it can be exactly the error you are trying to catch.
Where house lots meet this
A lot line that leaves a straight side line and immediately curves along a bulb often is nontangent at that corner. The corner is an angle point and the start of a curve at the same time. The frontage dimension is along the arc, and the side line is not radial unless the plat says it is. Read both facts. A measuring wheel along the gutter will not tell you whether the curve is tangent. County GIS simplifies both kinds of curve into similar shapes at screen zoom. Platbookmapper does not classify curves. If you are sketching for yourself, mark nontangent in big letters so you do not hand a tangent sketch to a designer. If you are building, the surveyor stakes from the full curve data, not from the sketch.
What to do next
- Look for the word nontangent or for a radial bearing.
- Do not assume the radius is perpendicular to the incoming line.
- Require a chord bearing or a radial bearing before you plot.
- Keep the corner’s angle and the curve’s start as two facts at the same point.
The mix-up to avoid
Running a tangent curve because the table showed a radius and an arc. Those two numbers are the shape. Tangency is a separate relationship to the previous course, and it has to be stated or proved by the bearings.
Questions people ask
Is a reverse curve nontangent?
A reverse curve flips direction at a PRC. Each piece may still be tangent to the piece before it. Reverse and nontangent are different ideas. A curve can be one, the other, both, or neither. Read the letters.
Can I tell from the drawing if the CAD file is gone?
Sometimes the kink is obvious, and sometimes it is a few degrees that a reduced plat hides. The bearings and the radial note are the test. A pretty PDF is not the test.
Find the county map
Start at Platbookmapper, search the county, and open the local GIS link. Write down the parcel number before you compare the screen to a paper plat.
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.