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Working on a road junction I would like to make a perfect rounded circle buffer of 1 km around this junction in QGIS 3.4. Here is what is look like now.

enter image description here

  • do you want your circle centred at the centre of the junction? – Ian Turton Feb 19 at 15:58
  • I need a circle of 1 km radius for every extremity of the road. – Nohan Feb 19 at 16:01
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    then you have that it isn't a circle (and can't be) – Ian Turton Feb 19 at 16:02
  • Is there another way to change this buffer (after being created) into a perfect circle? – Nohan Feb 19 at 16:03
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    depending on the intended use for the buffer, either A) you must keep this non-circular shape. or B) you can create a new point layer centered in the road features and then draw the 1km buffer (of course it will not, and cannot, be exactly 1km from all edges while remaining a perfect circle) If you want perfect circle you will have to compromise with the length measurements. you have to decide what is more important: precise distance measurements, or a nice looking circle. – Marshall Feb 19 at 17:14
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So, if I understand you correctly, go ahead The original data, see figure 1

enter image description here

create a polygon type from your data

2) Run the data analysis tool on it> Vector geometry> Minimum enclosing circles see figure 2 enter image description here

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If you start a new editing session you can create a new polygon circle that estimates the size of the buffer.

You can make it more exact by referencing the coordinate points at the far points of the buffer.

You won't be able to make a circle that is exactly the same distance from every extremity of the road because it is an uneven shape.

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1) Calculate the centroid of the feature. 2) Calculate the distance from the centroid to the farthest extent of the feature. 3) Make buffer that is 1 km plus the distance from step 2.

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