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I'm trying to get data from a polyline layer into a grid (I've created this with regular points, points to polylines). I guess at first I have to cut all polyline segments at the grid lines and then I have to spatially join (which only works for the first feature found) all of them into each grid cell. I want to find out road network length differences in different areas.

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Create a polygon grid using the Vector Grid tool instead of lines. Make sure to check the polygon output.

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Once you have a polygon grid (also known as fishnet), you can use the Sum line length tool in the QGIS Vector analysis tools. This will result in a new field for each cell with the total road length inside it

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Here's a simple example of a vector polygon grid with overlayed line layer.

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And after the sum lines in polygons tool, with symbology based on the summed length field.

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  • If I create a vector grid, what do parameters stand for? I guess they represent geometric resolution, but which scale units are used? I used 0,01 and in utm32 edge length seems to be 692 meters? – Revo May 1 '16 at 16:51
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    The grid size is dependent on your layer CRS. If you used 0.01 degrees in a geographic system like WGS, then that result fits the 692 meters you measure when projected to UTM. I used a metric CRS, and defined the grid size to be 100 meters in my example. Again, it all depend on your CRS and the spatial resolution you need. – HDunn May 2 '16 at 12:19

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