Adding values from two polygons

[TamarinGullett]

I am trying to calculate the number of fire fighters that can reach an area within seven minutes.  I created polygons of each seven minute service area.  The polygons overlap in some areas.  I want to build a model that will take the intersection of each overlapping polygon and add the value from each of the two original polygons together creating a new polygon with the sum of the two service areas.  Anyone have any ideas on how to do this?

[TamarinGullett]

Update:
The model I've built calls our Network Dataset, creates a new 7min service area, adds the firestations as locations, and then solves. I used select features to pull the resulting polygons, then copied them into a new shapfile called FireDistib, then joined the table with the staffing counts using the Station Numbers as the Key ID field. Easy enough.
The Intersect tool gives me the individual geometries of the overlapping areas, but I am desperately trying to avoid having to run things by hand as we are going to test different placements and staffing options.
Rasterizing the data may work, but I'm not sure which tool would add the values in the ShiftCnt field (which is a float field).
Still working, let me know if anyone has any ideas 😄

[CedricWannaz]

I am not sure that I fully understand what you want to do.. is it just to count all points that lie in each polygon defined by your 7 min service area, and output the same polygon feature class with an additional field that contains the count of points ?

If so, even if polygons are overlapping, you can create a join based on spatial location between the polygon FC and the point FC, using a Sum as a summary per polygon.

Regards,

Cedric

[TamarinGullett]

Hi Cedric

Thanks for your reply. There are no points. The number of responding firemen per station is stored strictly in the polygons.
Attribute Table looks something like this:

FID   ShftA    ShftB   ShftC   StatID
0         5           6        4          23  
1         6           6        6          21  etc etc 

Each station has their own set of numbers. I need to know how many people are available in the overlap areas... so where station 23 and station 21 meet/overlap, for that particular little area, we should have 11 people for shiftA, 12 people for ShiftB, and 10 people for shiftC.

The process needs to be able to run from a model because we will be running scenarios where we move the personnel around to different shifts and stations, there are too many stations (and overlap areas) for me to rerun this entire thing by hand every time a chief moves someone.

I hope this makes more sense.

[CedricWannaz]

Hi Tamarin,

    Are you analyzing the intersections only, or they are then to be related to the original polygon FC? And are there regions where more than two polygons can/will overlap? I am not the most experienced GIS user, but the following would perform what I understood from your last post (even if it is not very elegant), if overlaps happen between no more than two polygons at each location:

I assume that you have of polygon FC named "polygons", that contains the fields that you mentioned: ShftA, B, C.

1. Make a copy of "polygons", called "polygons_copy" for example.
2. Intersect both, keeping all the attributes. Say that the output is "polygons_intersect".
3. In Data Management/Layers .. use Make Feature Layer.
  - Choose the intersect as an input FC.
  - Build SQL expression "FID_polygons" < "FID_polygons_copy"
4. In the output, you can then sum by similar fields (e.g. create a field "ShftA_tot" and calculate it as "ShftA"+"ShftA_1").

Writing a script for this would take 10 minutes, but it might not be worth the effort for 4 operations.

If more than two polygons can overlap at the same location, things become a little more complicated.

Cheers,

Cedric