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Really bad plat
Posted by Hollandbriscoe on June 10, 2019 at 10:20 pmI have a question for the hive. I am doing a lot survey on a small parcel here in town an the only description I have for the property is being all of lot 4 of the attached plat. The lot 4 i am talking about is on the bottom of the PDF not the pie shaped ones above. For the life of me I can not figure out how to calculate the curve marked 150. It is not the radius and a 150 arc length wont work either. There is not a single radius on any curves on this entire plat. I am down to the point of using the back of the existing sidewalk and calling it a day. Any thoughts?
thebionicman replied 5 years, 4 months ago 16 Members · 21 Replies 
21 Replies

on the assumption it’s a tangent curve it would seem like you could easily calc the curves on either side of it and go from there.

Preliminary plat that was recorded before draftsman completed drawing.
In Block 7 the lots are not numbered.
Once some developers get their hands on a drawing they head straight to the recorder and file it as is and then fire the Surveyor.
As fit it to the rest of the Block and make the measurements work.
good luck

well, i still can’t figure out what bugs there are that keep my main account (flyin solo) from working like 98% of the time anymore, but here’s what i came up with for that curve, holding the stated bearing on the south line of Lot 5:
R=68.43′ D=125°35’20” ARC=150.00′ CB=N41°05’23″W CHORD=121.72′
looks like it is either nontangent or there is a +/ 2.5′ bust in there somewhere. that’s by building all the lot lines per B&D and constructing the resulting curves. (i got radii of 671.85 and 376.64 guessing they are supposed to be 670 and 375)

I don??t believe it??s a preliminary map, I think you have mentioned your from the Asheville area, we have three subdivisions here that look identical to the map you attached. My previous employer told me that someone from Asheville designed all three of ours in the seventies. If it was ??Scott? then I??m relieved we are not the only ones who have to deal with his crappy maps.
The maps we have scale reasonably well so we bring in pdf and find a radius that works with the arc length, and existing monuments if there are any. None of the curves appear to be tangential so I wouldn??t worry about trying to make them.

taking that, if you push a tangent reverse curve out from the northeast corner of Lot 5, holding a radius of 69.75 feet, that gets you within a couple tenths of the end of a 28′ arc shown on the north line of Lot 4.
another consideration being that, on your lot, you’re dealing with zero decimal places for record. so if i had nothing else and got to between .51.49 i’d be satisfied…

Jones
Unfortunately this plat was recorded in 1925. I run into these quiet often here in Asheville as nobody has updated the plats or deeds in a while.
A Harris the section you are talking about is actually off of the map and is part of another plat.
Thanks everyone. I am still trying to learn some things in CAD and fortunately these kind of problems don’t happen that often.

I zoomed in and printed that portion of the map, which came out to be 1″=60’±.
Holding a 70′ radius (based on three equal distances from the ends and middle of the arc) and measuring the delta with a small protractor, I got 123.5°± which gives an arc length of 150.9′.
I would need more information for that 28′ arc on the northerly side to calculate a closure.
I will go with chimeric’s answer.

How many corners have you found?

I have found all three corners so this is just a matter of making the arcs work, which I am finding is an area my education may be lacking a little bit.

Posted by: Dave Lindell
I would need more information for that 28′ arc on the northerly side to calculate a closure.
I tried to fit a curve to lots 1,2, 3, and part of 4 in order to learn more about that part of lot4. I find the radius to be a bit more than 400 ft maybe 408, but it doesn’t fit both the corners of lot 2, with one long and one short, different by 1.6 ft.
. 
Crossing the street and working out the radius on the opposite row might give you a clue as to what was intended. With the distances penciled in to the nearest foot though it might only be guide. At least it would be a thorough boundary examination.

We have plenty of old recorded plats similar to the example shown. Although one can (at times) calculate circular curves on these plats that fit the dimensional criteria given, I’m not so sure some of them were ever actually meant to be circular curves. I have seen a few plats that were most likely drawn with a French curve (an antique drafting tool).
Surveying within these plats can teach a surveyor a lot about understanding what was actually being shown on the document or implied by the document and what wasn’t. Assuming there is mathematical harmony and logic within some plats may just be wishful thinking.

That is a bad plat. Reminds me of a local subdivision that was created by an engineer that worked heavily on railroad projects a long time ago. As you can guess, all of the curves were railroad curves. Total pain assured for anyone who didn’t know the engineer’s history.

Paden, I agree wholeheartedly. This is part of the reason why I have the philosophy that curves are where the error lies

In the late 80’s I worked for an Engineer/Surveyor that had done many subdivisions just like that in the late 60’s and early 70’s. The party chief/old timer that did the fieldwork was still there and still the party chief. Those subdivisions were designed on the ground and surveyed enough to make a plat in the office. There was no design and go stake it out. Any distance that was not measured on the ground was scaled between the dots on paper.
That 150 foot is the length of the arc and may have been measured with a cloth tape sorta draped around the arc where they wanted the line. Forget math, there was none.
James

Remember stories of an old timer that staked the strait lines, then turned a deflection angle to the end of the other straight line. Once that was done cloth taped a distance and used curve table in field book to determine arc distance. Everything fit within a foot or so and nobody could measure the arc distance anyway.

Check the deeds. There are plats of this type recorded in the Portland area. Sometimes the lots are described by M&B in the deeds, thus filling in missing information.

Norman believe me I looked. The deeds all call for being all of lots from PB PG etc etc. except for the lot to the south, however the M&B is out so bad it was useless.

Any solution that does not take the field evidence into account is likely wrong.
It’s nice when records are neat and tidy, but they are only part of the picture.

I’ve seen many plats like this in Minneapolis/St. Paul. But I don’t remember seeing one where the lengths of the side lot lines were only given to the nearest foot. That’s unusual.
With the straight lines laid out and curves superimposed, I checked 7 or 8 of the side line dimensions against the curves. As shown on this .pdf, about half of them fit the curves within a couple of tenths. The other half miss the curves by 2 to 4 feet.
Some side line dimensions might have been laid out in the field to give starting points for the curves, but others might have been scaled. And as Paden said, a variableradius French curve might have been used to draw some of the largerradius curves. If so, that could have thrown the scaling off.
On the other hand, the arc/chord dimensions on Lots 13 and 57 of the subject block, and Lots 1822 of the adjacent Block 23, all check within a couple of tenths. It would have been very tedious to calculate those in 1925, which means they were probably measured. That means it’s likely that the curves were run in the field, and that in turn makes it likely that curves of even degree were used. I have used evendegree curves in this calculation, as shown.
Under this hypothesis, they could have turned angles for the side lot lines from the straight baselines at the rear of the lots, and set a couple of lath on each line for sighting. In running the curves along the streets, the chainmen would have chained each successive lot frontage on an estimated line, sighted themselves in on the lath, and called out an approximate chord distance to the Iman. He would have then adjusted the deflection angle. That would have been easier to do with an evendegree curve.
After setting the corner at the intersection of the deflection angle and the lath line, the chainmen would have remeasured the chord to tenths or hundredths, since those fractional feet must have come from somewhere. They probably didn’t distinguish between chord and arc on these largeradius curves.
The lot corners were probably all set, but they might or might not have been marked with irons due to their higher cost. Wood hubs would be more likely, but many of them could have been replaced with irons later.
The large curve on Lot 4 didn’t have to be monumented in the field except for the PRCs at the ends. But what the field crew could have done was to measure the chord, and also set up on each PRC and measure the angle from the chord to the tangent. Dividing half the chord by the sine of that deflection angle would give the radius of a tangent curve.
As I have it calculated, the radius doesn’t come out the same at the two PRCs. I get 69.78 at the northerly PRC and 70.76 at the southerly one. That means there is no single curve that would be tangent at both ends.
The field crew didn’t worry about tangency. They would have given the chord length and deflection angles to the draftsman. He in turn probably settled on a 70foot radius for the curve. He didn’t have to give the radius or otherwise explain it, he just had to draw it.
A nontangent 70foot radius curve would have an arc length of 155.56 feet, as shown. It overlays fairly well on the curve on the drawing, and the drawing scales pretty accurately elsewhere. The 150foot arc length was most likely a rough approximation that the draftsman came up with.
For comparison, I’m showing a curve having a 150foot arc (radius 73.78, purple line). It doesn’t fit the arc on the drawing nearly as well.
This curve is probably not going to be an occupied property line. There is no possibility of conflict with the neighbors, and only a remote possibility of a dispute with the City about the ROW location. And whatever way it’s run, it would be hard for anyone to prove that it’s wrong.
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