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

[JoseSanchez]

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

[DanPatterson]

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

Dissolve (Data Management)—ArcGIS Pro | Documentation

[jcarlson]

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.

[MehdiPira1]

@JoseSanchez ,

Try Dissolve instead of Union.

[DanPatterson]

That has already been suggested....

[JoseSanchez]

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.

[DanPatterson]

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