I have a polygon layer with every cities in my region. One of the field of this layer is the population of the city.
I also have a line layer which represents some bus route
I would like to automaticaly calculate the population concerned by the bus route (which means the sum of population of the polygon intersect by each bus line).
First of all how to calculate this in a new field on the line layer?
Second how to get this result to be update if the route change?