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How can I merge overlapping polygons (same shapefile) in ArcGIS 10.3 without losing polygon area, i.e. the total area of the new, merged polygon should equal the area of all individual polygons combined.

The individual polygons I want to merge are different parts of the same city - Berlin pre-WWII. I want to calculate the area of the city at that time. The city is spread over several old map sheets, which I had to georectify before digitising the city boundaries as polygons. Because of the age of the maps, the map sheets slightly overlap after being georectified, which means that the individual polygons that make up the city overlap as well. How can I merge these polygons into one polygon of the whole city without losing area?

  • quick dissolve tool – ziggy Apr 27 '17 at 14:52
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There is a Statistics Field in Dissolve. You can Sum the original Area or any Numeric Field during the Dissolve. Have you tested this option?

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Do you have the area of the originals in a field? The final area of the merged polygon will never equal that of the originals if they overlap - it will be less - otherwise the overlaps would be counted twice.

It sounds like you might want to be converting your shapefile into a feature classes. These automatically generate the area of a polygon.

  • Thanks for your reply. I added a little more context to my question. – MaikS Apr 27 '17 at 14:52
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It sounds like when you dissolve, you would want to uncheck the "create multipart features" polygons setting. This will preserve the individuality of the polygons but still dissolve them.

  • Thanks for your reply. I added a little more context to my question. So I would use the Production Dissolve tool (desktop.arcgis.com/en/arcmap/latest/extensions/…)? – MaikS Apr 27 '17 at 14:54
  • Are you doing ESRI Production Mapping for editing data? I was suggesting the typical Dissolve tool within the Data Management/Generalization toolboxes. You can also find it by selecting the Geoprocessing drop-down list at the top of the ArcGIS interface, dissolve is listed. – rachel.passer Apr 27 '17 at 18:55
  • Yes, you would do a dissolve, and I would think you'd just create a new field, and calculate geometry to get the area of the new polygons. Discrepancies from then on would more likely be related to the coordinate system/projection your data is in. – rachel.passer Apr 27 '17 at 18:58
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-You could try this after Merging:

  • Right Click on area field title
  • Calculate Geometry
  • Property: Area

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