I have a line vector file that displays a road network. Most roads consist of a double-line indicating the sides of the road (hence the width of individual segments), but some roads are indicated by a single line. Furthermore, many segments are open shapes, so a line to polygon conversion does not "fill in" the paved roadway correctly, but ends up creating random polygons across multiple road segments.

I'd like to calculate the total area of the paved surface of the roads but am unsure how to do this. If I were to calculate the length of the lines and then use an average width to approximate area, the length would be incorrect because most roads are represented by two lines - but some roads only have one line - so I can't simply divide the total length by two. There is also a lot of variability in the width of the roads.

Is there a way either to convert the lines to polygons - but respecting the "pavement" of the roads? Or another method altogether? I attached a screenshot to illustrate (the buildings are a separate polygon layer).

enter image description here

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    Oh, nice. This is a lot of manual work if you really want to do it correct.
    – Erik
    Oct 13, 2020 at 13:53
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    I originally tried to do a land use classification from Sentinel2 data, but there were a lot of incorrectly classified pixels because the urban areas are so variable. I don't have a lot of experience with classification though so I thought the vector files might be easier.
    – Matt
    Oct 13, 2020 at 14:06
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    The data is from the Carta Technica Regionale in Italy (link below). The road layers are in the "05_VIABILITA'" zip file. The line layers are the shapefiles that start with "05L_"etc. dati.lazio.it/catalog/it/dataset/…
    – Matt
    Oct 13, 2020 at 14:34
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    There is a processing tool, Split with Lines (processing toolbox -> Vector Overlay -> Split with Lines) which should help you but after having testing the tool with you sample data, it does not yield good results. See here: youtube.com/…
    – GreyHippo
    Oct 13, 2020 at 19:01
  • Might be useful to split the road segments into two categories based on their number of lines. 1. single line roads need a set buffer distance. 2. double lined roads need a different approach. Can the single lined roads be identified through the attribute table? Interesting question!
    – MarcM
    Oct 14, 2020 at 8:34


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