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Unit Conversion?

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(@jeff-austin)
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Does anyone have the conversion handy to go from GIS acres to "real" acres?

 
Posted : October 3, 2010 8:27 am
(@loyal)
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Sure do!

The equation is:

GIS acres x 1000 = dollars to SURVEY "real acres"

Loyal

 
Posted : October 3, 2010 8:42 am
(@james-fleming)
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> Does anyone have the conversion handy to go from GIS acres to "real" acres?
>
>

(GIS acres) x (Dangermond constant) = Real Acres

 
Posted : October 3, 2010 8:43 am
(@deral-of-lawton)
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Seems like a logical statement to me. They are supplying you an acreage based on the GIS. With the metadata then you can decide whether the values are valid or not. It could be based on a survey, deeds or something else. At least they are telling you to explore a bit deeper.

No different than the Tobins or other hard copy maps that we have used for many years.

 
Posted : October 3, 2010 9:13 am
(@perry-williams)
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An Acre is to a GIS Acre what a One Hundred Dollar Bill is to a Monopoly Hundred Dollar Bill.

 
Posted : October 3, 2010 2:32 pm
(@squinty-vernier)
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Ohhh...pretty colors. Multiply by magenta for surveyed acreage.

Srsly, one of our local tax mapping offices generally suffix's the area with a (c), for calculated. A disclosure that it was calculated by someone other than a LS.

Rick

 
Posted : October 4, 2010 1:40 am
(@mightymoe)
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We are lucky-don't need to worry about conversions they have it down.
This is the area from the local county GIS for last parcel I worked on:

AREA_: 6447659.00943456

square feet!

 
Posted : October 4, 2010 6:31 am
(@martin-f)
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Reminds me of when i was teaching GIS a few years back.

Although i'd never seen it mentioned in any text book, i decided it was important to distinguish between land parcel attributes that were more or less unchanged after a polygon overlay operation (which yields a set of smaller polygons), and those that need to be recalculated (because they depended entirely on a polygon's geometry). Examples of the former are soil type, planning zone class, taxation rates, etc, while examples of the latter are total area, total land value, etc.

I explained all this in a lecture, then a few days later in the lab, students were asking me why, after overlaying two maps and re-summing the areas, was the overall area increasing, dramatically.

It seems that the mighty ArcInfo was treating polygon area as a static attribute and, if a polygon was subdivided, each new part polygon would have the same area as its parent.

If only the Dutch would have had ArcInfo instead of going to all that trouble of diking, draining, and desalting, they could have had geometric growth in land area simply by doing a few polygon overlays!

 
Posted : October 4, 2010 8:20 am
(@daniel-s-mccabe)
Posts: 1457
 

Well that was a very GISey thing to say.

 
Posted : October 4, 2010 8:26 am
(@mightymoe)
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Cool so I could buy that 148 acres the county says is there; split it into ten lots then sell 1480 acres-I could make a fortune!

 
Posted : October 4, 2010 9:14 am
(@jim-in-az)
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The fact that this question can even be asked sends shivers down my spine...

 
Posted : October 4, 2010 9:27 am
(@mightymoe)
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I just had to check after these posts.
Just finished two parcel resurveys of existing tracts on friday for a closing that happened at 3:00 PM.

The GIS acreage for the first tract = 43.11 Ac.
The surveyed acreage = 42.71 Ac.-not bad

The GIS acreage for the second tract = 39.69 Ac.
The surveyed acreage = 37.07 Ac.-not so good.

I suppose that is typical but I just never pay attention to the GIS acreages; now I'm curious.

 
Posted : October 4, 2010 9:29 am
(@jeff-austin)
Posts: 121
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I agree.

I was looking at buying this parcel and got quite a laugh out of the "boundary information" provided by the realtor. LOL!

 
Posted : October 4, 2010 9:44 am
(@guest)
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Could also work towards a landowners advantage if the GIS Acres was above the min. required for a parcel split and that was all the planning department used to approve it.

 
Posted : October 4, 2010 1:18 pm