California Surveyors Forums

It is my understanding that industry standard for survey data precision on a subdivision map is to the hundredth of a foot. I cannot recall seeing a map that showed survey data precision to the thousandth. I also have not seen subdivision map showing a combination of measurement data to the hundredth and to the thousandth. The city mapping ordinance does not address the precision requirement, it only states that the accuracy of all measurements and angles turned should be within 1:10,000.

My question, "Is measurement data shown to the thousandth a standard practice to account for summation errors on curves due to round-off for subdivision maps?"

My initial position is to say no, but I would like to open a peer conversation on the subject.

As a standard practice I don't go to 3 decimal places. But every once in a while it makes sense.

In regards to subdivisions, I have no idea. But on RS maps and in legal descriptions I have shown curve deltas to the nearest 0.1" because the radius was so large (30,000') that 1 second was 0.14' in arc length. It was impossible to show closure with less precision than that. Same for ties to CGPS stations for control networks.

I'm not sure there would be a difference between a subdivision map or any other kind of map.

If we are being completely realistic & honest, although reporting to the nearest hundredth and to the nearest second is and has been standard for quite some time, in nearly all instances that is beyond the accuracy that we can achieve. For a network of points and lines, the ALTA/NSPS standards are pretty realistic at 0.07' +/- 50 ppm.

Many years ago, I worked for a surveyor who would not label any direction to a greater precision than the nearest 10", although he did report distances to the nearest 0.01'. If it weren't for paralegals, title officers, and county map checkers having a fit if the dimensions don't close within 0.01', that would still be a very valid labeling standard for final mapping.

Labeling to the thousandth is just silly and not at all reflective of achievable accuracy or precision under the best of circumstances, using very tight procedures and highly specialized equipment that an average surveyor has never even seen, much less used. The only reason I can think of a reasonable LS putting a distance to that precision on a map is to get it past a particularly anal map checker whose mathematical sensibilities have been offended because a closure resulted in 0.02' misclosure, and that map checker is lacking in adequate professional supervision.

Good grief.

1 minute is 1/60th of a degree. Tan 1/60 = 0.00029. Multiply by 100 ft = 0.029 ft per 100 feet.

1 minute error (or no error) in 100 feet amounts to 0.03' deviation from true course.

Ten seconds is 1/6 of 0.03' in 100 feet...

Are we getting anywhere yet? Follow the footsteps of your predecessor, unless the dipshit goes to the 1/6 minute or even stupider the 1/60 minute..

The concept of mathematical closure is a myth in reality. We cannot measure to such an accuracy is to close a traverse, and we cannot create a true line with three points. Impossible in reality.

Any call to less than 1/4 minute on a map is pure garbage, mathematical nonsense...

when I see distances reported to 0.001, my first question is always, Can you truly measurement that? Did you use the correct methods and procedures to be able to proof those results? And usually it is not likely. Even reporting to 0.01 could be challenged on most surveys. IMHO

Dunno, I just think some of you over-react. I like the .001' precision just because you always get that .01' misclosure that you have to put somewhere in CAD, so I suspect some people just like to extend the precision so you can deal with the rounding errors. Fine with me. I do not presume the surveyor thinks he can measure perfectly in the field. I dislike it when the block proration leaves lots 50.006' each,and we round up, so you then the map checker points out a .01' issue somewhere since things do not add up.

I do not think it is something to get that worked up about. There is actually a subdivision map in Burlingame from the 1920s I believe, that has .001' precision. I am sure the guy did not think he could pull a chain that well.

That's when I use it. Given the choice of arbitrarily choosing one of a set of prorated distances to be different than the rest, I'd rather show them all to 3 places. Big deal. I'm not making any claims about measurement precision. Now, if all the distances on a map are to 3 places, that's another story.

By showing that precision, you are implying to any who view the map and don't know better that you have measured to a greater degree of accuracy than others. Surveyors (mostly) know better. Most non-surveyors (and some surveyors) don't.

I like to place a note on maps to the effect of:

"Due to rounding, the sum of individual measurements may not equal the overall measurement." Some jurisdictions accept this. Others...

When I see thousandths of a foot or tenths of a second reported on a map I can't help but think the surveyor who prepared the map was working with an unreasonable map checker, something I've dealt with in certain jurisdictions.

I like that!

As a private surveyor, I only go to three places when a map checker says my individual pieces do not add up to the whole by a hundredth of a foot or one second of arc.

As a map checker, if the pieces do not add up to the whole, but are within a hundredth of a foot or one second of arc, I know it is because of rounding and I do not mark it for correction. As long as the closures are good and they all fit together like a puzzle.

On my private maps. if the map checker finds and marks a case like this for correction, they rarely find them all.

In some instances you could spend the rest of your life chasing down a hundredth of a foot or one second of arc, because when you change one, then another total whole may not add up.

I had a couple of RS maps submitted to a county that were Metric maps and the checker was seriously giving me grief over one or two millimeters in stationing versus the measurements. Some notes that I made back to the map checker - A - Stationing is per the plans, not my calcs. B - You realize that 1 mm = 0.003 feet right? He was chasing these minute distances around these maps for two or three checks before I got the County Surveyor involved, who put another checker on it.

One city required 3 decimals on a map I did, which had been the standard practice of the local surveyor for over 50 years. I can state from experience that chasing around rounding errors through curves is no easier than with 2 decimals, and I now resist all such requests.

Funny about the MM stationing...

Yes, 3 places sometimes also no better at totaling the whole, but then I ask the checker if they are really worried about totals being out 0.001' and that has worked so far. I know the same should be for 0.01' too, but sometimes it just takes that extra decimal to convince.

I have also checked a map where prior to submittal, the submitting Surveyor had already gone through and tried to reconcile all the pieces to the totals and so had changed his map such that it no longer matched some of the closures, which I did mark for attention. I actually hadn't realized he was trying to total the wholes, but I always mark everything that does not match the closures. So I guess you can be damned if you do and damned if don't depending on who is checking the map. The submitting Surveyor really wanted his totals to add up, so I let it go, knowing the reason his closures were off only 0.01'.

The submitting Surveyor did not catch all the places that it occurred on the map, but I did not bring any of that up. Poor Surveyor could spend the rest of life tracking down hundredths.

Map checkers here will make you chase the hundredth between the parts and the over all. You have to fudge something, somewhere. And then that doesn’t agree with the ACAD closure calcs. I have been missing those old school COGO programs like LLCOGO where you typed in the data shown on your map and get a closure of say 0.02' but it is also 1 part in 500,000.
As much as I dislike ACAD 2015-C3D, it does allow me to input old style closures. Not sure if the County is going to buy them when they see a hundredth or two, but at the same time they are all way, way better than 1:10,000.

Well then there's the problem of small 100 SF cusp shaped parcels, that simply will never close to better than 1:10,000.

This discussion is another example of technology unduly influencing the surveying profession. The folks that are checking maps are not surveyors; they are a bane to the surveying community if they feel these types of standards are to be imposed on map makers.

This has nothing to do with the art of surveying. It has to do with computers dictating policy and the user not knowing the difference.

Time permitting, this is a topic that needs to be explored, discussed, and then eliminated. This is the theme of my article noted in another post.

To be sure, it is a bit sad and can only lead to bad things.

The further I develop my practice in California I am discovering that the things that really give a survey map value are not notes documenting evidence and conditions found in the field or detailed communication of methodology.

What makes a good survey here is standard curve data, open circle symbols for set pipes and closed circles for found pipes and your leader lines better not cross each other.

Also, you're probably not really a land surveyor unless your college has an ABET accreditation or you are employed by the DOT