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once and for all: what is the most accurate way to calculate the area of intersecting polygons (i.e. how much of one polygon is within another)?

Question asked by aurelies on May 16, 2018
Latest reply on May 24, 2018 by MervynLotter

This is probably the most important operation anyone has to do with GIS: calculate the area of something within something else. I can't think of a single day when I don't have to do this. So why is there no reliable method?


I am calculating the total area of forest within provinces and districts. I don't use tabulate area because you have to convert the outputs from m2 to something else and it's a pain. I saw the Summarize Within tool in ArcGIS Pro and thought gee that does exactly what I need. 

All my data are in cylindrical equal area projection.


The results I get from using Summarize Within however are greatly different from if I clip my polygon to a province area and add geometry attributes with geodesic area. We are talking large differences here - 20% or more. I have lots of provinces and districts and clipping to each one will take an eternity. 


How are people supposed to reliably calculate area if the GIS tools provided give completely different results? Is there reliable information as to which tool to use and which is more accurate? I am wondering now how much error there are in all the forest area reporting out there when using different tools seems to create huge differences.