California Surveyors Forums

Jim Frame wrote: Mon Jan 31, 2022 11:24 pm

all lots must close by less than 0.017'

...with allowance for rounding.

I recently filed a ROS that used a couple of CORS for a bearing base, with a short tie (1600') from one of them to my boundary. The CS asked for a closure for the triangle, the long side of which was about 70,000 feet. I usually balk at what I consider to be silly requests, but in this case I complied. I hadn't computed the tie from my boundary to the distant CORS, so I just forced the closure in CAD. (I even labeled the closure sheet "Forced Closure.") With bearings rounded to the nearest second, that skinny little triangle closed by just under 0.2'.

0.017 closure is a bit silly. I know a number of mapcheckers are hung up on that number.

Rule (in orange county) reads ... 1:20,000 or 0.017
The reason for submitting closures in the first place is so that the mapchecker has something to use to proofread the map numbers and eliminate typos and flip-flopped numbers. Closure must match the the map in a number of decimal places. 1:20,000 is there to show that you are only dealing with the rounding error. Closures need to be done to 2 decimal places for distances, and to the nearest second, same as annotated on the map.

With insistence on 0.017 by some mapcheckers and their lack of understanding of closure precision and people who can't get past splitting hundredths, now we have people submitting closures showing three and four decimal places for distances, and decimal seconds to one or two decimal places, so they would fit the 0.017. It defeats the purpose of even submitting them.

The way measurements and math system was initially set up (lot of us learn this in college classes), you measure to a tenth, you calculate to a hundreth (and when using coordinate alcs, you calculate to 4 decimal points), so that your calculations don't dilute your measured values with rounding errors. Or, what we did in europe, in the metric system, if you are doing measurements of 4th and 5th order (+/- about 1cm, depending on whose order definitions you are using), you will perform your calculations to a millimeter (3 decimal points). If you are dealing with more precise measurements, you may expand your notations by an extra decimal point. Especially in the older days when you were using logarithmic and sin tables and doing calcs long hand. You expand the number of your decimal places to accommodate significant figures.

It is difficult enough to have conversation with most surveyors about mere existence significant figures, and even less so about how to apply them in practice, or in rule making.