I am using ArcGIS Desktop 10.5.

I have a shapefile for impervious surfaces and a shapefile for tree canopy. I need to separate the tree canopy features into tree canopy that overlaps (is assumed to be above) impervious surfaces vs. tree canopy that does not overlap any impervious surface, and specifically I need to be able to calculate the area of each. Ideally I'd also merge these layers together to get a single shapefile that shows tree canopy over pervious cover, tree canopy over impervious cover, and impervious cover with no tree canopy above it, with the ability to calculate area for each class.

Here's a screenshot of what I have so far:

layer of trees and layer of impervious surfaces

How can these shapefiles be merged so to create a unique feature or attribute wherever the original shapefiles' features overlap?

  • If you also want impervious cover with no tree canopy above it, that would mean an area where they don't overlap. If that's really what you want then a union overlay would work after recalculating your area fields.
    – John
    Mar 16, 2018 at 20:00

1 Answer 1


The geoprocessing tool that does this is union. It will merge both geometries and split them wherever they overlap.

You get unique features for each type of overlapping or not. The attribute table hold all columns from both layers. In the attribute table you can then select all features that are either tree or surface or both. Have a look at the tool help if it fits your task.

  • 1
    Perhaps you mean union, because intersect will remove canopy outside impervious area.
    – FelixIP
    Mar 17, 2018 at 4:16
  • I think this is the correct answer though I actually used intersect. Was having some problems with union for whatever reasons, but intersect processed correctly. I was able to take the area for each layer of interest & the intersect of them to calculate all the areas I ultimately needed.
    – cr0
    Apr 4, 2018 at 14:57

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