once in a while I have to layout property lines for a project site. The few times I have had to layout a site plan, I have run into problems getting the property lines to close...
sometimes I don't have a "legal description" and a "surveyor's Plat" at the same time to go by. Usually I only have a "plat"
I don't know what your drawings are used for, but you are treading on dangerous ground if you are not working under a licensed surveyor. Simply showing a dimension from a property line to an existing building is illegal in the state where I live unless prepared under a surveyors supervision.
Where did the plat come from? How do you know if it is right? Without the legal description, and knowing how to interpret the description, you cannot verify the plat.
Has the property been surveyed, position of monuments determined, compared to record, and any discrepancies been resolved? If you go forward with design, you might get an unwelcome surprise when it comes time to build and the lot is really smaller than you thought...
modern survey methods measure these plus or minus 0.005 feet and [angles] within 1/2 second and there can be significant accumulated error within these tolerances
Modern survey instruments can indeed be this accurate, but the rodman (and instrument man) is not. You cannot hold a prism pole perfectly vertical, a good rodman can consistently hold the rod over a point to within 0.02 feet horizontal accuracy under good conditions, 0.005 feet is simply not realistic.
The errors in general do not accumulate, they are random unless you have a systematic error in the measuring instruments.
For instance, draw a line on a piece of paper.
Now measure it with a scale that has very fine gradations, like 1"=80' engineer scale.
Record the distance. Repeat measuring, say 100 times.
Sometimes you measure too short, sometimes too long. If you average all the measurements, you are closer to the true measure of the line, not farther. The random errors don't add up, they tend to cancel out.
A legal survey will almost certainly have this rounding error accumulate through the boundary courses
The mathematical closure of a parcel is calculated in the office, not measured in the field. The parcel should close within tolerance, or whoever is checking the description before recording is not paying enough attention. If you find a description which does not close, it should be brought to the attention of the surveyor to resolve what should be done.
(I work as a surveying technician)
C. Roberts