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Kent1Cooper
en respuesta a: Anonymous


@Anonymous wrote:

.... for an as-built plot plan of a facility. .... how accurate should we expect measurements on a drawing to be?


I have no simple answer, but some thoughts....

 

This may not be exactly what you're asking, but in my experience with such things, if I lay out a property boundary in AutoCAD using metes and bounds numbers along the edges in a drawing like that or from a deed description, an "accurate" survey will not come out at the end of going around exactly at the starting point unless it's something simple like a rectangle, but it is typically within about 1/16" [in US Imperial units -- that would be about 1.6mm] of the starting point, maybe twice that much in something as big as 15 acres.  If the drawing comes from modern surveying techniques, you should expect that kind of accuracy, at least in property boundaries, if not maybe quite that precisely in existing features locations.

 

I agree with others that it depends on what it's for.  If you need to work in parking spaces and a lane to get to them, and there's a regulation about the size of the spaces and the width of the lane, then it really matters how much space you have to work in, possibly to within as little as an inch or so if it's a close fit.  Or if you're trying to fit another building in, it matters from the point of view of Building and Zoning Code requirements, when there are setbacks and fire-separation distances to account for, and I would want things to be similarly drawn within inches of truly precise.

 

There is a certain degree of "reasonableness" to the issue.  Even if a drawing of existing conditions has the corners of buildings [what a Surveyor would typically locate] very accurately positioned, it may have the walls between those corners assumed to be, and drawn as, straight lines, but they may not actually be, so the distance between walls away from the corners may not be accurately reflected everywhere.  That's not likely to be very far off, though -- they're not likely to assume a straight wall unless it's pretty close to that.  Or, for certain features, you can't expect too much precision, for example, where do you draw a tree with a sloping trunk in a plan?  At the ground plane?  Four or five feet up from the ground, where they typically measure the trunk diameter?  If the ground rolls gradually from a more level area into a bank, where is the "bottom" of the bank?  Etc., etc.

Kent Cooper, AIA