Calculating mean distribution of point locations using field values in QGIS

Question

I have a layer of point locations distributed country-wide. I would like to create a new point layer that shows the mean or center of mass of the points, but grouped based on the value of a field, such as province or municipality. Thus we have the mean coordinates of the points within each province or municipality.

How do I do this in QGIS?

Answer 1

One can try the "Mean coordinate(s)" geoalgorithm.

Computes a point layer with the center of mass of geometries in an input layer.

An attribute can be specified as containing weights to be applied to each feature when computing the center of mass.

If an attribute is selected in the parameter, features will be grouped according to values in this field. Instead of a single point with the center of mass of the whole layer, the output layer will contain a center of mass for the features in each category.

Let's assume there is a point layer called 'points_test' with its attribute table, see image below

Fields:

"id" : a unique identifier
"Group" : a grouping field for points (corresponds to your province or municipality). In case you do not have these values, please use additionally the "Join attributes by location"
"Weight" : a field with weights

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How does this geoalgorithm work?

I. Using the geoalgorithm without checked fields

It will return just one dot (a yellow one).

II. Applying only the 'Unique ID field'

It will result in one point for each unique group, check the red dots

III. Setting both the 'Unique ID field' and the 'Weight field'

It will result in one point for each unique group based on the points' field with weights, see the green dots

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One should always distinguish between:

• a midpoint
• a centroid (a geocentroid)
• a center

Only in specific (and rare) cases, they are equal.

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References:

• Getting the line middle point with SQL in QGIS
• Finding mean coordinates of cluster of points from point layer in QGIS