# Over-calculation of area due to parcels occupying same space

I'm trying to get the total acreage of different parcels by land use, and unfortunately I keep getting a total of ~15000 acres instead of ~12000 because it's over-calculating the area where there are condos or other multi-units (two condos sharing the same parcel area are being counted twice instead of once). It's basically calculating the total acreage as if each condo were occupying its own land when in fact they're both occupying the same space.

How can I calculate the total acreage only on the ground level without double counting? I don't think I can combine the attributes because I would lose data on how many occupants there are.

• Are your condos represented each as the entire parcel or are there child parcels inside the main parcel for each condo? – Adam Kara Apr 29 '16 at 17:41
• They're each represented as their own parcels. – Meia Apr 29 '16 at 17:44
• !Picture. Here's a sample pic of the two condos selected. – Meia Apr 29 '16 at 17:52
• What if you dissolve the parcels and in the Statistics Fields you could calculate the sum for occupants (if you have that information in the attribute table) and/or do a spatial join on the dissolved layer with parcel (which would give you the count of parcels in the dissolve area). You could also use intersect to split the dissolved parcel layer by land use area and then do the spatial join on parcels to get the information you need – crld Apr 29 '16 at 18:34
• What GIS software are you using? – PolyGeo Apr 29 '16 at 21:29

## 2 Answers

Yikes. It's amazing to see the poor practices in place when creating parcel sets. There's a couple easy options here revolving around creating a copy of your feature class. You could make your selection, export to a new FC and then run a merge if you only have to calculate one use. If you need to find the areas for all of your land uses I would still create a separate feature class and merge each land use together. This will dissolve your overlapping parcels and give you a more specific feature class to work with while keeping your original parcel FC together.

• Thanks Adam! Will try the second option as I need to find the areas for all land uses. Will post update soon. – Meia Apr 29 '16 at 17:55
• Some of the counties I get parcel data from do what you're experiencing for multi-tenant properties like duplexes. I've done the process I just mentioned to have a feature for land use and one for zoning. – Adam Kara Apr 29 '16 at 18:01

The vertically separate, but 2-dimensional overlapping parcels have to combine and accumulate both units and occupants. To collapse them to a single 2-D building parcel you need to do the following.

Extract the centroid of the parcels with the Feature to Point tool and keep all attributes

Use the Spatial Join tool with the parcels as the target and the points as the join. Use the One-to-One setting. Set up the field map to get a Join of the Parcel Numbers with a delimiter (a concatenation). https://esriaustraliatechblog.wordpress.com/2015/06/22/spatial-joins-hidden-trick-or-how-to-transfer-attribute-values-in-a-one-to-many-relationship/

Now you can dissolve on the concatenated Parcel Numbers (drop the original Parcel Number) and you can get the sums that you want of occupants in only one shape that ignores floor separations.