Lately I have been using the Mapcheck routine in Civil 3D to check the closure of a parcel being created. The routine uses the displayed measurement of the line/curve to calculate the closure report, i.e distances to the nearest hundreth and directions to the nearest second, and not the precise measurement of each line/curve. The routine then calculates the area of the parcel based on the polygon defined by the displayed measurements. In some cases this area is not the same as the area calculated using the area command on the closed polygon.
So which area do you use? The perfect cad area or the area based on the displayed measurements that would be shown in the legal description, or on the face of the map.
I doubt the difference would be outside of the significant figures you should be reporting area too. Say you have a 466.69'x466.69' (5 acres) track as dimensioned with actual measurements of 466.695' on a side. The resulting areas would vary by around 4 sq. ft which is at least 10x less than the minimum area I would report on a ~ 5 acres.
But to answer your question, push comes to shove I would report the unrounded value.
Map check can be different, I use the polyline that I put around the parcel. But I always round quite a bit, I will show .01 acres but never .01 sq feet. Usually with Sq. Ft. it's the nearest 10.
The issue I am running into is that some government agencies are now requiring the closure report to be included with that map submittal, and it the areas don't match up extactly, they reject it.
There is your answer. You have to go with the mapcheck area. Like John said the difference is not likely significant. If it seems to be you may be reporting too many decimal points.
The issue I am running into is that some government agencies are now requiring the closure report to be included with that map submittal, and it the areas don't match up extactly, they reject it.
Hmm. If mapcheck says a million square feet you're not putting that on your survey are you? I assume most guys would convert that to acres. Converting to some other unit like that might get them to back off?
The agencies in my area require a map check report too, but I haven't had them nitpick the survey and mapcheck values matching exactly. I'd probably just try telling them the survey isn't a binding document so it doesn't matter what it says on there.
That or I'd try fiddling with the mapcheck settings to get it to report the same precision I show on my survey.
I did some work for a government agency that required map checks along with area in square feet and acres. The map checks had to close no matter what size and how many breaks to less than .01’ ft. Also all coordinates had to be given to the nearest.01 of a foot. Bearings nearest second. As all of you are aware I had to do some serious checks. The he other wrinkle was everything had to be in both NAD83 state plane and nad27 state plane along with ground distances also. It really became a numbers game at the end put a second here round up there blah. Blah blah. Sometimes it was just frustrating to be honest.
This is nothing more than mathematical masturbation.
I've had my eye on this topic for a few days. It's hard for an old fella like me to believe it was raised. We never ever trusted linework for calculations but maybe things are different now. We always kept a record of the mathematical area calculations for each parcel.
There has never been a reason not to trust linework, as long as you verify its integrity. If the creator just used CAD to sketch a concept (read artichoke or engineer) then you need to make sure the linework is correct. Garbage in, garbage out.
One company I worked for would do a comp check set of plats. Before recording a set was plotted and we computed the whole plat fresh using just the info on the plat. We checked closures, coordinates, areas, curve data. It was a good way to catch little mistakes.
The closure report should just serve as a check that the information shown on the map is correct. The horizontal misclosure is always reported and everyone is happy if it comes out to 0.01' or less. However it seems there also needs to be a miscolure for the area, 0.01' over a distance of 600' is 3 S.F. They all seem to think that the area reported on the closure report is the correct area.
@antcrook which government agencies? Report your areas as required by the real governing body. Never report areas in feet unless required. State your area and state more or less. Be sure you understand the accuracy of which you are certifying.
@antcrook .01’ over a 600’ leg MAY induce up to 3 feet of error in area, but only if the.01 is perpendicular to the 600’. It never is- because that is a representation of the accumulated rounding in every leg of your parcel. There are probably larger sources of error in your closure than the .01’ when you think about it. Are all you corners nice capped monuments? Any stones? Any fence corner posts? any low water mark? The reviewing agencies need to look at do the courses in the legal match the courses on drawing, which need to match the map check courses- and if the area reported in the legal is reasonably close to map check in regard to rounding.
I understand the map closure concept, I am trying to figure out a creative way to explain to the bureaucrat with their clipboard and checklist as to why the closure report area and map area don't always agree.
What size are these parcels, and what units are being used to describe them?