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Polygons merged when added to topology

joebuck

Using ArcMap (ArcGIS Desktop 10.8.1) on Windows 10 Enterprise 64-bit.

I collected 322 polygons in Field Maps using a GNSS unit. A polygon represents an area of a stream (pool, riffle, or run). Then I exported the polys from the hosted feature layer to a FGDB. The original coord sys was unchanged (WGS84 Web Mercator Aux Sphere). Then I created a feature dataset in the FGDB (same coord sys) using defaults and imported the polys. The polys look fine at this point. Then I created a topology on the polys in the fdataset with rule "Must Not Overlap". After validating the topology, many of the polygons are now merged with adjacent polygons. The number of polygon features did not change, but many if not all of the polygons now have multiple overlapping parts. Why did this happen?

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Accepted answers

joebuck

The solution was to run Repair Geometry. Several polygons had "incorrect ring ordering". After repairing, the topology found a few legitimate overlapping polygons that were easily fixed.

All comments

joebuck

Same thing happened again with polys exported from the Arcgis online hosted feature layer to a shapefile, then imported into the feature dataset, then added to the topology. The polys are fine until they are added to the topology, at which point they are getting merged. The attached gdb contains an example of the original unmerged polys (polys_no_topo), and after adding to a topology (polys_topo), which caused polys to be merged.

polys.gdb.zip

joebuck

The solution was to run Repair Geometry. Several polygons had "incorrect ring ordering". After repairing, the topology found a few legitimate overlapping polygons that were easily fixed.

qnadeem

I just faced the same issue, I think issue is being generated from the shape file conversion, as shape file cannot handle the same precision as of geodatabase. running repair geometry can solve this issue.

GISJess

I just experienced a similar issue in ArcGIS Pro. Thanks for sharing.

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