I need to Single Sided Buffer a specific surface based on a line length, on QGIS.


  • line length: 60.367 meters.
  • area needed from single sided buffer: 452.4 square meters.
  • theoretic Single sided buffer value: 452.4/60.367 = 7.49 meters.

Issue: On corner where the line turns at any angle, I lose some of that surface. For example at a 90 degrees with the values mentioned theoretically I lose 7.49 * 7.49 = 56.10 square meters.

I have tried to modify the formula by: area_needed/line_length + buffer_value^2.

But even that addition loses some surface trough lines buffer intersection, thus it would have been needed an iteration until surface matches perfectly.

In the example below, the intersected surface is lost:

enter image description here

Question: How do I solve the buffer value calculus from dividing surface needed by line length, to something consistent that adds up the missing surface.

Additional Edit:

As mentioned below: By "summing up the missing area in all these intersections - adding this to the area needed and recalculate" it increases the buffer value but it still does not reach the desired area.

enter image description here

It seems I lose some surface with buffer parts that are outside the polygon within I measure that area. Also, buffer being perpendicular with the generating line and not with the polygon where area is measured within.

2 Answers 2


Have you tried to sum up the missing area in all these intersections - add this to the area needed and recalculate?

  • I have tried this and it adds up to the original value. I thought that the surplus value is also affected by this intersection and it still does not reach to the desired value. But now as I think more of it there is also missing surface due to the fact that some of buffer parts are not within the desired polygon and also due to the fact that buffer is perpendicular with the line and not the polygon within area is measured. Commented Jan 16 at 9:47
  • I have added an additional edit to be more clear with my comment. Commented Jan 16 at 9:50
  • Somehow i need to sum up also the polygons that are outside the polygon, then it might solve my issue. Commented Jan 16 at 9:51

I have solved it by:

(area desired + missing area from intersection + missing area outside the interest area polygon) / line length.

enter image description here

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