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enter image description here

I'm a new user of QGIS 3.10.4. I need to create contours on maps using buffer, union and dissolve functions in QGIS. The buffers will be from multiple points.

Is there any way I can unionize and dissolve all the buffers at one go?

I have been using union for 2 buffers at a time and its taking me some time to complete my task.

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    If you use the buffer tool, you can check a box that says that buffers should be dissolved. For the rest, the question is unclear to me. Add additional information, ideally a screenshot of what you want to do.
    – Babel
    Commented Jan 6, 2022 at 11:10
  • Yup, I'm using that at the moment. The main problem is, i have 3 groups of data that have multiple point source in them as shapefiles (distance for the contour is jointed to 3 csv files). So when I create buffer for all 3 groups, i need to unionize them to create a continuous contour. QGIS only allow 2 sets of data to be unionize at one point. I'm looking for alternatives so that i can unionize the buffer created from the 3 groups at the same time (will add more groups in the future) (added picture for clarification)
    – zaido141
    Commented Jan 6, 2022 at 11:23
  • I think the easiest way to combine various algorithms is the graphical modeler: docs.qgis.org/3.16/en/docs/user_manual/processing/modeler.html And I don’t really understand what your task is. But it sounds to me that maybe you could use the merge tool instead of the union tool first and then use other tools like dissolve or union?
    – Motti
    Commented Jan 6, 2022 at 11:50

1 Answer 1

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You can visualize a series of different, dissolved buffers using Geometry generator with this expression (in line 3, adapt the list of different buffers sizes):

collect_geometries (
    array_foreach (
        array(0.5,1,1.5,2,3,4,5),
        eval (
            'buffer (collect(buffer ($geometry,'  ||  
            @element  ||  
            ')),0)'
        )
    )
)

Based on the point layer (red points), different buffers in different colors are created using the expression: enter image description here

If you want to style each distance differently, enclose the expression in a segments_to_lines() function (see documentation) and then use data driven override for different aspects of the style (color, stroke width etc.), based on the variable @geometry_part_num:

enter image description here

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