topic Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer in Geoprocessing Questions

Union in Model Builder does not merge polygons. It copies them as they are in the source layer

JoseSanchez — Wed, 03 Nov 2021 21:18:17 GMT

Hello everyone,

I am looking for a way to merge all the polygons with a specific condition in another polygon layer.

I am creating a feature layer with a subset of the polygon feature class and when I run the Union the final result does not merge the polygons I selected.

This is what I am doing

in Model Builder

- Select all polygons from FC grid polygon that are located in Area =1

- run Union tool

This creates a new FC that shows the same subset, not the expected result only 1 polygon.

What am I missing?

Thanks

Jose

Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer

DanPatterson — Wed, 03 Nov 2021 21:24:25 GMT

When you say 1 polygon, do you mean....

Dissolve (Data Management)—ArcGIS Pro | Documentation

Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer

jcarlson — Wed, 03 Nov 2021 21:24:47 GMT

I'd suggest reading through the Union documentation, but the image from that page sums it up well enough:

What you are describing sounds more like Dissolve Boundaries.

Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer

MehdiPira1 — Thu, 04 Nov 2021 00:39:57 GMT

@JoseSanchez ,

Try Dissolve instead of Union.

Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer

DanPatterson — Thu, 04 Nov 2021 01:25:29 GMT

That has already been suggested....

Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer

JoseSanchez — Thu, 04 Nov 2021 12:33:11 GMT

Thank you for your answer Mehdi and Dan,

I am confused because with ArcMap I am able to select the same out put layer, open an edit session, select all the polygons form my select, run the Union and it merges all the polygons in one.

So the Union in ArcMap does not work the same way as the Union in ModelBuilder.

Re: Union in Model Builder does not merge polygons. It copies them as they are in the source layer

DanPatterson — Thu, 04 Nov 2021 17:47:31 GMT

An edit session is a different environment than modelbuilder and their behaviour isn't the same