Problem solved w/ JOIN

The Problem In the Nature study I suggested that the Schools would prefer a 50/50 split between Forest and Ag cover The solution to this common problem… That is, how to compute percentages of cover, elevation values, slope values, for polys in a FC (like Tax Parcels)

Assumptions This works best with data in GDB but as long as you are willing to keep calculating Areas it will work with standalone Shapefiles There are scripts for area calculation GDB is the better option, however

How to do it… To solve the problem of cover types in parcels you need to… Intersect Cover (input) and Tax Parcels (intersect features) (could use Union as well)

Aside If you are working with FCs that have large attribute tables you need to do the following… Copy the FC into a new GDB Review the fields (properties) Get rid of those you do not need by un-checking their check boxes (actually easier to un-check all and then check the ones you want o keep. This just makes life easier!!!!

How to do it… To solve the problem of cover types in parcels you need to… Intersect Cover and Tax Parcels Result is that each Parcel is broken into 1 or more polys based on Cover Like this…

Parcel 91294 is selected

Multipart Poly But, did not include the poly with the same code at the lower right????? The intersection created one multipart poly of 5 parts

Intersection table

Total area Stats

So far, So good How do we calculate what % each intersect poly is on a per parcel basis???? Remember – you can’t calculate BETWEEN records Where is the parcel area? Its is the Tax_Parcel FC!

Duh! Its in the Tax Parcel data! Parcel Area

OK, how to get it into the Intersect table? JOIN the Attribute table of the Intersection layer with the Table of Tax_Parcel data based on Parcel-id This is a one to many join Which means that the parcel record is joined to every record in the intersect layer that has the same ID

Now… Oops – minor detail. You have to create a new float field to the intersect table BEFORE you do the join! You can’t be in edit mode to create the new field and have to be in edit mode to calculate values

Calculate values The new field (made before the Join!) has the name pct-cov

Ta Da

Procedure… Put data needed in a GDB Intersect the selected parcels FC w/ cover FC (right one first!) Add a new field to Intersect FC for % Calculation Join Tax Parcel Attribute table to Intersect FC table Calculate %