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Is there a tool or plugin in QGIS that resembles ArcGIS 10's Dissolve tool? I'm trying to dissolve several polygons (parks) around the boundaries of another layer of polygons (cities), while performing various calculations for multiple attribute fields (like summing their total area, doing a count of features, etc).

I looked into an earlier question (Batch Dissolve Polygons based on Attributes in QGIS or FWTools) where ftools was recommended, but ftools doesn't allow you to specify the way you would like to summarize statistics for multiple attribute fields. Is there one tool that allows me to summarize statistics for multiple attributes, like the ArcGIS Dissolve tool?

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    In conjuction with dissolve, try using the Group Stats Plugin. It allows you to get several calculations (count, area, perimeter). You can then export and join the result to your dissolved layers. – Alexandre Neto Jul 10 '13 at 16:20
  • dont know arcgis, but have you tried vector->geoprocessing tools -> dissolve in qgis ? – Kurt Jul 10 '13 at 18:12
  • Yes, but QGIS dissolve doesn't let you summarize statistics of different attributes. That being said, when I do try to dissolve my parks file (I have a lot of duplicate rows) around their individual feature ID's, the dissolve tool freezes up and QGIS shuts down. Any suggestion as to how I might dissolve the file around an attribute-- so that I can get rid of duplicate rows-- without making all of QGIS shut down? – Alex Jul 10 '13 at 18:16
  • is there any update on this feature request? this is THE feature that I miss most and hence, that prevents me from entireliy shifting to QGIS! it would be great to direcly implement the summarize function into the dissolve tool! cheers – user30142 May 12 '14 at 9:41
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There is a new QGIS plugin called dissolve with stats, which provides the functionality you are looking for.

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You can also try SQLite/Spatialite (comes with QGIS) or PostgreSQL/PostGIS where dissolve "a la ArcGIS" is done by the combination of the ST_Union() function on the geometry and a group by on the attribute to be summarized.

Something like this:

SELECT ST_Union(the_geom),
    sum(st_area(the_geom)) as aggregate_area, 
    count(the_geom) as number_geoms 
INTO dissolved_polygons 
FROM your_table 
GROUP BY your_attribute;
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    I have voted this answer up, but you should add an example of how to "summarize" some fields, like it was asked by Alex. For example, include "sum(st_area(the_geom)) as area, count(the_geom) as count" in the SELECT code. – Alexandre Neto Jul 11 '13 at 8:47
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In QGIS 2.10, there is a feature for computing the statistics by categories (like ArcGIS summary statistics). Go to processing > toolbox, the geoalgorithms > vector > Statistics > statistics by categories. You can the join the resulting table with the dissolved layer. I must warn that after the join the numeric fields are interpreted as text fields, so this is not so handy (you need to compute a new field with to_real() or to_int() )

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