[Qgis-user] plugin to find boundaries around points

[Nyall Dawson]

On Mon, 10 Dec 2018 at 03:42, Holly Allen <h-qgis at antiform.com> wrote:
>
> I've stumbled onto QGIS through a work project, and have a specific problem I'm trying to solve. We have a set of around 5000 locations which are broken up into about 500 districts. We'd like to produce a map of polygons representing the districts, and I would really, really like to not do that by hand if I can.
>
> I've poked around in QGIS a bit (mostly 3.4.2, but I also installed the latest 2.x version briefly to check it out) and worked through the list of plugins available, and I don't see a way to auto-generate boundaries between groups of points. I am about to write the code myself, but wanted to ask the group whether I'm just missing something obvious. Please point me to anything I'm missing! Since I haven't done anything in this field before, I may simply not be searching for the right terms. Bonus points if I can take the resulting boundaries and have them snap to state boundaries (in another layer) wherever the state boundaries happen to fall between the groups.

My suggested approach:

1. If you don't already have "districts" assigned to the points, run
the DB Scan processing algorithm to auto-assign points to a logical
cluster
2. Run voronoi polygons on the points
3. Dissolve the voronoi polygons based on either the existing district
field (or the cluster id assigned by DB scan)
4. Run the "snap geometries to layer" tool to attempt to realign the
dissolved voronoi polygon borders to your existing state boundaries
(within a suitable distance tolerance)

Nyall


>
> Thanks,
> Holly
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