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# Dissolve with statistic field sum returns unexpected result

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02-23-2012 09:41 AM
New Contributor
I have a bunch of building footprints that I'm trying to calculate actual area of each individual building. The 'actual area' is calculated by multiplying the shape area by the number of floors.

When I dissolve the footprints into simplified shapes, I'd like to aggregate the actual area of the building footprints into the new footprint. I'm using the SUM calculation on the the statistic field of the actual area, but it's returning the area of all the buildings in the dataset, not just the single building's actual area.

For example, a two-story house with a single story addition. The two story shape area is 1000sq ft. The single story addition area is 500sq ft. I am looking for an 'actual area' value of 2,500sq ft (2 floors of 1,000sq ft, and 1 floor of 500sq ft), but ArcMap is returning the area of ALL the building polygons in the dataset, and attaching that to each individual polygon.

Can someone help me out here?
Tags (3)
7 Replies
MVP Emeritus
The dissolve is working in the x/y direction and not what you want which is individual x/y/z's
New Contributor
My understanding is that the SUM calculation of the dissolve feature is aggregating the area of all the building areas into one result, rather than calculating it on an individual building basis. The polygons resulting from the dissolve all share the same area value.

Is there a way I can calculate this attribute on a building-by-building basis instead?
Regular Contributor III
Unfortunatly, the Dissolve tool in ArcGIS always dissolves the geometry into Multipart features and then (if you want) breaks it into Singlepart features - which works properly "most of the time". To be sure, always run the MultipartToSinglePart tool on the Dissolve tool output.

So more direct to your issue.... As you disscovered, the Dissolve statistics always describe the Multipart shape  - not (like you might think) the derived Singlepart shapes.

There is a work around though. The idea being that if you can tag yourt input features with a sort of unique spatial ID and Dissolve by this derived ID value, then your statistics come out the way you envisioned: describing the single part features. See attachment for latest rendition of some Python code that I wrote that does just that.
by
Deactivated User
Unfortunatly, the Dissolve tool in ArcGIS always dissolves the geometry into Multipart features and then (if you want) breaks it into Singlepart features - which works properly "most of the time". To be sure, always run the MultipartToSinglePart tool on the Dissolve tool output.

So more direct to your issue.... As you disscovered, the Dissolve statistics always describe the Multipart shape  - not (like you might think) the derived Singlepart shapes.

There is a work around though. The idea being that if you can tag yourt input features with a sort of unique spatial ID and Dissolve by this derived ID value, then your statistics come out the way you envisioned: describing the single part features. See attachment for latest rendition of some Python code that I wrote that does just that.

Hi, I am a new hand working on a customizing dissolve tool and trying to get some idea from your code.
One question, the PARAMETER_DATA_TYPE of networkIdField and selectionMethodd is text? Cause I only get the "text file" in the list. Or it is "string"?
I am using 10.1
Thanks
Regular Contributor III
Yep - Those would be a Data Type of String.
by
Deactivated User
Yep - Those would be a Data Type of String.

Thank you very much
by
Esri Regular Contributor

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