Geographic Information Systems Stack Exchange is a question and answer site for cartographers, geographers and GIS professionals. It only takes a minute to sign up.
Sign up to join this community
I have a number of bus stops (green points) and a layer of population data (square polygons) containing information on the number of households.
I want to know how many households are within the 500m buffer of the points.
How do I sum the attribute (number of households) to a new value for each point?
Here are a couple of ways to sum up the total value of intersecting polygons.
Install the refFunctions plugin, and use the Field Calculator to add a field to the buffer layer with this expression:
intersecting_geom_sum('population_data_layer','number_of_households')
Use the Field Calculator to add a field to the buffer layer with this expression:
aggregate( 'population_data_layer', 'sum', "number_of_households", intersects($geometry,geometry(@parent)))
Notes:
within or within_geom_sum instead of intersects or intersecting_geom_sum. Or, as johns pointed out in the comments section, you can re-calculate the value based on the proportion of the area of each square that intersects the buffer. This assumes that the households in each square are evenly distributed throughout the square. It's probably a better approximation of reality than the approaches above. See this and related questions for how to calculate proportional area:
intersecting_geom_sum and aggregate functions. The aggregate functions were relatively new at the time I wrote this answer, so they may have changed syntax. Or perhaps they changed the spelling on the other function, eg perhaps they made it intersecting_geometry_sum instead. If it's only a minor syntax change, you should be able to fix it by re-creating these expressions using the built-in help in the Field Calculator.
My solution was the following
Now the buffers have a new attribute with the total of households.