meanpointpoint-creationqgis
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?
You need to do this in a two-stage process using the Vector > Analysis Tools > Mean Coordinates tool in the second step. This tool will return the mean coordinates for sets of point within a layer if they have a unique "ID" field. So, if you have a polygon layer which defines your areas, do a spatial join (Vector > Data Management > Join attributes by location) to attribute your points with the polygon (area) id and then use the Mean coordinates tool, specifying the new field.
You may already have unique "ID"s or a polygon layer but if you do not you could create a fishnet (Vector > Research Tools > Vector Grid) to lay over the points as one method to define the areas. Alternatively, if your areas are defined by a raster layer, then you could use the Point sampling plugin to attribute the points based on your raster. Or, if you want to attribute them by location without a vector or raster layer, you will need to create an algorithm to give a new attribute based on the coordinates of each point (possibly using some modulus-based approach).
This is an example trying to mimic your situation. Please modify layernames and field names according to your project.
Above figure shows two layers: Fire point layer with size field, and Grid layer with id field only.
Start Field Calculator on the Grid layer, and give this expression:
array_mean(overlay_contains('Fire', expression:= "size"))
It will return averaged fire size. (It returns null where you do not have any fire).
Best Answer
One can try the "Mean coordinate(s)" geoalgorithm.
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 weightsHow 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
One should always distinguish between:
Only in specific (and rare) cases, they are equal.
References: