ArcGIS Pro: Merge Failed. Cannot merge overlapping polygons with differing Z values

Error Message

When merging overlapping polygons using the Merge tool from the Modify Features pane, the process fails and returns the following error message:

Error:
Merge Failed. Cannot merge overlapping polygons with differing Z values.

Cause

The vertices of the overlapping polygons are at different elevations (z-values) relative to the ground surface. Merging polygons with different elevations leads to an inaccurate representation of the surface. Therefore, by default, ArcGIS Pro does not allow the merging of polygons with different z-values.

Solution or Workaround

Check the 'Merge z-aware polygons and allow non-planar geometry' check box

To merge polygons with different elevations and nonplanar geometry, check the Merge z-aware polygons and allow non-planar geometry check box. This option enables merging polygons with z-values while preserving accurate elevation information. Refer to ArcGIS Pro: Allow nonplanar geometry when merging z-aware polygons for instructions.

Remove the z-values from the polygons

If the polygon features are 2D and do not require elevation values for analysis, remove the z-values. This also allows for editing feature layers in other ArcGIS applications, such as ArcGIS Online or the ArcGIS Enterprise portal. To remove the z-values, refer to How To: Remove z-values or m-values from a feature layer in ArcGIS Pro for instructions.

Assign a z-value to the overlapping polygons

Alternatively, assign a unique z-value to only the overlapping polygons. This method ensures the other polygon features within the same feature class retain the original z-values. Refer to ArcGIS Pro: Edit vertex z-values for instructions.