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I have two polygon shapefiles--blocks groups (BGs) and neighborhoods. Generally, BGs are smaller than neighborhoods. Sometimes they lie entirely within a neighborhood, but often they overlap two or more.

I can merge these so that the first joining attribute (neighborhood) is retained, but this isn't what I need. How can I join these two files so that the attribute table contains a row for each BG-Neighborhood pairing, with a variable giving the proportion of the BG contained in that neighborhood?

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Assume that in following image polygon1 green shapefile is a neighborhood an it is overlapped by blue buffers (blocks groups). By using field calculator determine area for each feature block group; as it can be observed at attributes table.

enter image description here

Run Intersection tool (Vector -> Geoprocessing tool -> Intersection) for BGs and neighborhood (polygon1) to get it and determine feature area in same way as above case.

enter image description here

Join to Intersection layer, by id, BGs layer. Result is as follow:

enter image description here

By using Field calculator determine overlapping percentage as follow:

enter image description here

Result is:

enter image description here

and layer must be saved with another name to preserve changes.

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