5

I have a set of locations each representing a service capacity. I also have a polygonal layer with each polygon representing local demand for that service. For each location, I would like to define its service catchment by summing up the demand values from its nearest polygons until they meet the service capacity of the location. I thought it might be easier to rasterize the demand layer and then do some cost distance assessment but I can't figure out how to do this by summing the attribute value to meet the local service value.

Image 1 shows the data I have, The location example has a service capacity of 1100 and the polygons represent local demand. Image 2 shows how I have manually selected polygons summing to close the capacity, this would represent the service catchment.Image 3 shows a rasterized version of demand

Image 1.

Image 3

Anyone have an idea how this could be achieved?

Image 2

1

This sounds like a problem for PyQGIS. I'm a total Python newb, so it would take me a very long time to actually code this, but I outlined a possible solution in pseudocode.

# Add a unique identifier field to the point layer (if it doesn't already have one)
# Add a field to the polygon layer, ServiceLoc, to keep track of which service location is associated with each polygon. 

# create a number variable, totaldemand
# create a number variable, buffersize

# for each point in the service location layer, do the following:

    # while totaldemand is less than the service capacity of the current point, do the following:
        # increase buffersize by some value (approximately the average width of shapes in the polygon layer)
        # create a buffer around the current point of size buffersize
        # select all polygons that intersect the buffer
        # set totaldemand equal to the sum of local demand values in the intersected polygons
    # once totaldemand is equal to or greater than the service capacity, change the ServiceLoc of all selected polygons to the unique identifier of the current point
    # clear the selection

The same basic plan could be used to set up a model in the graphical modeler.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.