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Having the following information in a CSV file:


I want to build a polygon with all the points where the Group name is the same.

For example I want to join all the points where the group is T101 and form a polygon.

How can I achieve it using QGIS? enter image description here

marked as duplicate by Dan C, whyzar, Jochen Schwarze, xunilk, Fran Raga Feb 21 at 8:19

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  • 1
    Just concatenate your Group x,y,x,y,x,y in the correct order (clockwise?) +make sure x,y start and end is the same coordinates. – Mapperz Feb 19 at 21:03

Connect the dots method:

  1. Use the Points to path tool to draw a line connecting each set of points. Use your field called "group" for the Group field.

    Make sure the points are connected in the correct order, IE going around the outside of the polygon rather than zig-zagging back and forth.

    enter image description here

    If you have the second case, the next step will create invalid polygons. Go back and create a field you can use to force the points to path tool to join the points in the correct order. If your data doesn't have a convenient way to create this field, this may not be the best method. Try the method below.

  2. Use the Lines to Polygons tool to convert the lines into polygons.

Concave hull method:

  1. Export the point layer, and choose "multipoint" as the geometry type.

  2. Use the select features by value tool to select all points in a group, and merge them into one feature. Repeat for each group.

  3. Run the Concave hull (k-nearest neighbor) tool. This will create a polygon for each multipoint feature. This works best for simple polygons. If your polygons are very complex, it may simplify them. For example:

enter image description here

In that case you would have to manually edit the polygon.

  • I used the first method and it worked correctly, thank you. Now I have a question, how could I add the name as a polygon property? I am trying to create a GeoJSON with the polygon layer and I need to have the name as property. I would appreciate your help too much. – Gibrán Feb 20 at 15:14
  • 1
    there are lots of ways to do that, an easy way is with a table join gislounge.com/working-with-tables-mastering-qgis – csk Feb 20 at 17:41

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