If you just run Intersection with FIELD as input and TOWN as overlay you will get the data you need. You could join the TOWN and results layer using a key. Is there a reason you need to use an expression?
On Thu, Jun 24, 2021 at 9:43 AM Edouard Bourgine <edouard.bourg...@acosol.fr> wrote: > Hi, > > > > I’m running qgis 3.16 on w10. > > > > I have two vector layers with multiple entities : > > · One with each town borders (? I’m note sure if this is the > right word) I mean the area for each zip code. (TOWN_LAYER) (polygon vector) > > · The second with cropfields and meadows (polygon vector) > (FIELD_LAYER) > > > > I want the total area of cropfield and Meadows in each Town from the first > layer. (Exemple : one town have 31 fields/meadows -> total town area is > 55km² (i have that info) and cropfield/meadows area is 26km² (i need that > one for each town) > > > > First i tried something like : > > · > Sum(area(intersection($geometry,geometry(‘FIELD_LAYER_ID’))),group_by :=FIELD > WITH SAME VALUE EVERYWHERE) > > > > But it is not a valid expression (geometry(‘FIELD_LAYER_ID’) don’t work) > > > > Some meadows span over several town. Some juste inside one. > > I’ve « cut » the FIELD_LAYER with the TOWN_LAYER > > > > My first vector layer as a field specific and i’m looking for the formula > that would give me the right answer. > > > > I’ve tried : > > > > · aggregate (layer :=’FIELD_LAYER_ID’, > aggregate :=’sum’,expression :=$area, filter := intersects($geometry, > geometry(@parent))) > > > > It doesn’t work because the borders are overlapping : each fields just > touching the borders even if they belong to another town are included. > > > > « Contains » instead of « intersects » doesn’t work either because some > borders of the field are overlapping and those are not included. > > > > Exemple with « count » instead of « sum » > > > > A town have 31 fields spanning over 26km² : Intersects give me a total > count of 38 and 48km² and contains give me 12 and 4,7 km² because of > borders overlap. > > > > I think the solution is with intersection, but i can’t reach a valid > expression. > > > > Another solution may be splitting the FIELD_LAYER in as much layer as town > (I did that) and batch process for each layer : > > · sum($area,group_by := FIELD WITH SAME VALUE EVERYWHERE) > > > > then get the result in the TOWN_LAYER. > > > > But i don’t know how to batch process it and get the result in the first > layer. > > > > And for informations I’m talking hundreds of towns and thousands of > fields/meadows entities so one by one calculation is not possible. > > > > I hope I make sense and that someone know how to deal with that. > > > > Thanks, > > > > *Edouard BOURGINE* > > *Ingénieur Environnement* > > > > Tél/Fax : 03.83.22.69.09 > > Port : 06.63.12.99.63 > > > > ACOSOL > > 26 rue de l’Ornain > > 54520 LAXOU > > > > > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> > Garanti > sans virus. www.avast.com > <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> > <#m_4845219931750753823_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > _______________________________________________ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > List info: https://lists.osgeo.org/mailman/listinfo/qgis-user > Unsubscribe: https://lists.osgeo.org/mailman/listinfo/qgis-user > -- Drew French (715) 986-8088 www.ecologicaldesign.land
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