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I have this dataset that describes the cycleways of a city.

enter image description here

I want to measure the km of cycleway for each type of highway (residential, track, unclassified, ecc) and then calculate the percentage of km for each type (eg. if I have a total of 100 km of cycleways, 10 of which are paths, the percentage of paths is 10%)).

note: the geometry is a polygon

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  • you wrote a note: geometry is a polygon, what are you referring to, please explain better.
    – pigreco
    Feb 6 at 16:37

2 Answers 2

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To get the km of cycleway for each type of highway, use this expression:

sum("lunghezza", group_by:="highway")

To get the percentage of each highway type, use this expression:

sum("lunghezza", group_by:="highway") / sum ("lunghezza")*100
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You can create a virtual layer with the query:

select  row_number() over() as id,
        highway,
        sum(lunghezza) as lunghezza_sum,
        sum(lunghezza)/sum(sum(lunghezza)) over () * 100 as percentage 
        from yourpolygonlayername
        group by highway

enter image description here

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  • what does the query "row_number() over() as id" do? I'm doing a project with QGIS for my thesis so I need to understand what I'm using. this works perfectly by the way, thank you
    – anea
    Feb 7 at 12:24
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    It just adds a row count, 1,2,3, .... It is to get a unique id column. I think QGIS wants one or it throws an error when trying to create the virtual layer.
    – BERA
    Feb 7 at 12:26

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