[GIS] Intersect/union two different polygon layers to produce a third polygon type

arcgis-10.2arcgis-desktoparcmapintersectionunion

Can anyone instruct me on the correct way to union/intersect two different layers containing polygons so that a third layer is created containing the attributes of the non-overlapping regions from each original layer and a new 'class' or feature for any regions that do overlap? I am using ArcMap 10.2.2

For instance, see in the image below:

enter image description here

I want the areas that overlap between the purple and green polygons to be considered a new dataset. I know the "Intersect" tool in ArcMap would produce this "overlap" dataset, but only after stripping away everything else right? On the other hand "Union" produces what we see below. Is there anyway to do exactly what I am talking about? Or do I have to do an intersect, generating an isolated "overlap" layer, and then intersect this "overlap" layer with the other two (one at a time) to finally end up with three different layers separated into the information I want – after which I would merge them back together.

Best Answer

After running your Union, open the resultant Attribute Table and I think you will see that all polygons of overlap have IDs from both input feature classes that are >= 1 whereas where there is no overlap one or other ID will be 0.

Use the Select (Analysis) tool to select the polygons with both IDs >= 1 out into a new feature class and you should have the overlap feature class that you are after.
Use the Select (Analysis) tool to select the polygons with ID1 = 0 out into a new feature class and you should have the first non-overlap feature class that you are after.
Use the Select (Analysis) tool to select the polygons with ID2 = 0 out into a new feature class and you should have the second non-overlap feature class that you are after.

Related Solutions

[GIS] PostGIS Union Between Two Tables, Preserving Attributes

Without knowing your column names, this is my best guess. (I have not had a chance to test, so it may not be exactly right.) Hopefully you can suss out the column names I used. Assuming L is a subset of U:

SELECT l.id AS l_id, u.ab AS uab, l.abc AS labc, ST_Intersection(u.geom, l.geom) AS geom
  FROM u, l
  WHERE ST_Intersects(ST_PointOnSurface(l.geom), u.geom);

[GIS] Intersect Multiple Layers

Here is one approach that I think would work for you.

1.) Add a unique field to each of the input polygon layers.

2.) Populate each field with an identifier you can easily associate to that species.

3.) Iteratively run the Union tool for each layer union-ing to a master polygon layer. Now all of these unique fields will be included in your output polygon data set.

4.) Create a new text field in your output feature class.

5.) Use the python parser in field calculator to create a list of the species present in the polygon.

Something like:

speciesList = '[ {0}, {1}, {2},...,{13}]'.format(!field1!, !field2!, !field3!,...!field13!)

Best Answer

Related Solutions

[GIS] PostGIS Union Between Two Tables, Preserving Attributes

[GIS] Intersect Multiple Layers

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