# Over calculation of area- How do I calculate correct acreage when there are stacked parcels?

I am currently interning for a county in the United States. I am working on the data and mapping needed to fulfill the Open Space Activity of CRS. Stacked parcels are causing me a massive headache.

As an example, take a condo community we have here. It is represented by a parcel for the land/condo association itself, and then individual parcels for each unit are stacked on top this. This is causing the acreage for such areas to be doubled, tripled, quadrupled, etc. Any ideas on how to get around this problem?

Hopefully, these pictures provide a bit more clarity of my problem. In the drawn image, the blue numbers would be parcel IDs. And represent yet another issue of smaller stacked parcels within a large parcel representing the manufactured home park or condo community boundaries.

I have also attached an image of a problem area from the actual data set. It is only a sample of a much larger data set.

I know from dissolving the feature without basing on a field (producing a single polygon) that the area should equal 26.3 acres. The stacked parcels cause the area calculation to equal about 210 acres.

FYI, if it helps, for the Open Space CRS credit I need a table with a unique parcel ID, parcel owner, parcel acreage, parcel acreage within the special flood hazard area, and open space acreage of eligible parcel.

Open space credit is determined by dividing the acreage of eligible open space by the acreage of the regulatory floodplain and multiplying by 1450. I hope this all makes sense.

https://imgur.com/a/KpJHww6

• What GIS software are you using? What precise steps have you performed? – PolyGeo Dec 3 '18 at 10:05
• Is there another dataset you can use like land use? Although that might be at the city-level instead. Hmm. – mkennedy Dec 3 '18 at 17:48
• @mkennedy I could use land use as I do have all that data at the county level, but I can’t lose the unique strap/parcel ID. – M.Oliveri Dec 3 '18 at 20:39
• @PolyGeo I am using ArcMap 10.6.1. The steps I have taken are as follows... Dissolve parcels based on strap> converts dissolved polygons to points (centers in)>spatial join points to dissolved parcels layer>dissolve by join count>spatial join to points... I realized dissolving by join count is problematic because there may be multiple areas that have the same number of points joined to a polygon but those areas are spatially exclusive. I also am unsure what to do with the final output. At the end of the day, I need the correct acreage without losing any unique straps – M.Oliveri Dec 3 '18 at 20:46
• I think I need to dissolve down to get only the bottom parcels in order to get the correct acreage and then relate the points to those polygons but I’m really not certain. – M.Oliveri Dec 3 '18 at 20:47

My interpretation of your question is "how do I remove all the interior parcels and retain only the outermost polygons?" If that's right, try this:

Assume that the layer is called parcels. Right click, copy. Right-click on the dataframe (Layers by default) and click paste. Rename the pasted layer to parcels_copy.

Right click on parcels and select "Joins and Relates"->Join.

In the dialog box select parcels_copy for the "layer to join to this layer" in 1.

Under 2, select the second option - "Each polygon will be given the attributes of the polygon it falls completely inside of ..."

Under 3, name your new layer, maybe something like "outermost_parcels". Click OK

Right click on your new layer and click Open Attribute Table. Click Select by Attributes (either from the menu button at the top right, or from the correct icon on the top). Assuming the field "strap" from your sample data is unique across features, your query is strap = strap_1 (The attribute table will show fields strap and parcels_copy_strap. However, this latter field name is too long to use in a query and I think will be substituted with strap_1. Check the list of field names in the Select by Attributes dialog).

You now have select all the outermost parcels. You can now either create a new layer in the current map by right-click on outermost_parcels ->Selection->create layer from selected features, or right-click on outermost_parcels->Data->Export Data. In the dialog pick Selected Features and fill out the rest to suit your needs.

You'll end up with duplicated fields that you will want to clean up.