Slope, surface area, and acerage?

[Henro]

Curious and nothing more...

But I came to believe after reading some posts here at TBN that acreage calculations are based on flat area, for lack of a better term, and that if one owns land on a slope, that he will have more surface area than another who owns perfectly flat land.

Is this the case?

I believe my property is defined by degrees, minutes and seconds at each corner. It is a rectangle. It is slightly sloped.

I assumed that if the corners were projected upwards to a point in space that was a two dementional plane, and level, that the area calculation would be correct at that point, rather than being based on linerar measurements along the line of the slope.

Otherwise, around here, when people move mountains to make the land flat, for the sake of building a shopping center for example, they would also be decreasing the amount of the property they owned when they changed the lay of the land from sloping to flat.

What am I missing in the equation? Besides the fact that I don't even know how to ask the question properly? /forums/images/graemlins/blush.gif

 

[Soundguy]

Yes and no. If the properety is flat but sloped, it will still be the same surface area. however.. say it is flat.. but has a mountain inthe middle.. you obviously have more surface area than the guy that has a piece of property next to yours that is flat.. but has the same width and length.. etc.

Soundguy

 

[Robert_in_NY]

I know what you are trying to ask. I have been wondering the same thing. To clear it up a little (if I am correct) what you want to know is if a guy can own 10 acres of land on the side of a mountain but because of the steepness he only owns 100' in from the road and a 200' down the road. Does the land get surveyed as if everything was flat and if you have a mountain then you are lucky and have more surface on your land then the neighbor. Am I right? If so then I would like to know to because when we drive thru PA that is all I think about when I see all those hills with for sale signs on them.

 

[DKinWA]

I'm involved in reviewing logging plans in washington state and the Dept. of Natural Resources uses two acreage numbers on forest practices. The first being the acreage based on the standard flat dimensions and the second called "GIS acres" which includes slope calculations. For those unfamiliar with GIS, it's short for Geographic Information System. It's essentially a computer model of the earth which can be used for a variety of land management activities. By incorporating GIS acres, you get some idea of the additional volume of timber that will be harvested from the sloped ground. Hopefully, this provides some insight to your question.

 

[Henro]

<font color="blue"> By incorporating GIS acres, you get some idea of the additional volume of timber that will be harvested from the sloped ground. Hopefully, this provides some insight to your question. </font>

To ask the question using these terms...Does one purchase "flat acres" and end up receiving "GIS" acres?

I think the answer has to be yes...

In soundguy's example, the two same sized properties (identical, or congruent to use the term from geometry that I probably can't spell right) would be the same number of acres, even if one had a mountain in the center of it, which added a lot of GIS acres, right?

Follow up question:

If a survey shows two stakes 1,000 feet apart, then this would be a horizontal distance, independent of slope of the land, right?

And if a simple measurement were made by laying a tape on the ground, rather than holding it level between the two points, if the land is not perfectly flat and level, then the tape laying on the ground will always measure a distance greater than the 1,000' indicated on the survey, right?

I know I am asking the same thing over again, but thick brained ones like me take longer to learn than some... /forums/images/graemlins/grin.gif

 

[DKinWA]

Henro - Yes to your questions and yes you understand what I was trying to say. I'm not a surveyor, but this is the way one explained it to me. With the exception of measuring roads, distance measurements in the woods are almost always made using "horizontal distance". As I sit here typing this, it does make a lot of sense. Just think of the monumental task of surveying property in the 1800's if they had to account for hills and valley's. I'm sure just running the lines was more than enough to keep the surveyors busy for a long time.

This is one of those cases where a picture is worth a thousand words. Too bad I don't know how to draw and attach one /forums/images/graemlins/blush.gif

 

[DaveNay]

</font><font color="blue" class="small">( To ask the question using these terms...Does one purchase "flat acres" and end up receiving "GIS" acres?

I think the answer has to be yes...)</font>

I think the more fundamental issue is that you are buying a parcel of land. Since property is sold as an entire unit, then you are actually getting what is bound by the legal perimeter description, and not what is decribed by the area of the parcel. As long as you like the piece of property, then the actual area is ancillary.

Dave

 

[Wannafish]

Henro,
Yes, you get more "Surface Area" with slope(s) than "Square Footage Area". An acre is supposed to be measured in a level, horizontal plane.

I like to think that all the hills I have produce more (such as corn/hay/whatever) than if it was flat due to the greater amount of surface area. Of course the offset is all the extra fuel required to traverse the hills, so even when I think I'm ahead - I'm behind /forums/images/graemlins/blush.gif

 

[rtimgray]

Surveying is usually more correctly referred to at plane surveying, meaning that everything is considered in the same plane, thus dimensions of hills, mountains, holes, etc. are thrown out.

There have been folks around here that are selling their 10 acres and say "we'll throw the hills in for free".

I assume that the plane surveying came from "back in the day" when surveying was done with rods and chains, and it was hard enough to close a survey while doing it in plane fashion without even considering the true surface area.

Or maybe surveyors think the world is flat?

 

[phd]

Although surveyors are well aware of the difficulties of applying an orthogonal model to a spherical shape, they pretend things are locally flat. Most day to day boundary surveying remains in the horizontal plane survey as you say. Each country, or state or province will make some educated assumptions based on all the variables associated with the sphere to plane model transformation in their region and fix the grid. Larger scale mapping surveys have to make allowances for anomalies particularly at the edges of these orthogonal models and will sometimes resort to geodetic models (latitude and longitude) and sometimes apply a ground to grid factor of varying amounts (about 0.4' per 1000' locally). However, area as defined in almost all boundary surveys is, as was mentioned, in the horizontal plane and has no 3d component. Engineering analysis will sometimes require surface area where run-off and rate of slope are important factors. For the layman the techique of reducing a survey to a series of right angle triangles is the best area approximation.
Not a surveyor but that's my understanding,
Peter