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How could I create a buffer for each set of points (colour group) separately and in one procedure in QGIS 3?

The image below shows a subset of points for buffering.

In your Attribute Table, you need to create (unless you already have it) a field which will define the unique buffer distance for each of your points.

Then you will be able to accomplish the buffering process by applying

Vector > Geoprocessing Tool > Variable distance buffer

Elongation:

• If I have correctly understood the question gist, you are able to execute buffering "separately" by choosing the "Selected features only" in the "Variable distance buffer". Selected features can be achieved through the basic "Selection by Expression".


• Be careful with units. The buffer size is always applied in the layer CRS units.


• There is a way to accomplish this task with MMQGIS plugin.

I provide a short practical example based on Airports data from Natural Earth.

In Attribute Table of the Airports layer, I will use an already created attribute "wdid_score" which is an integer type and looks like distance in meters.

Then (after CRS adjustment) I proceeded with Variable distance buffer. See image below.

References:

• Variations in buffering


• Understanding QGIS buffer tool units?


• Does QGIS Buffer Tool use units of CRS? [duplicate]