I have an input vector polygon layer which has different areas. Now I want to join a different vector polygon layer which contains over 1 million 100x100 meter squares with information about the population.
As a result I want to see which part of the squares belongs to which area of the other polygon and also have the sum of the population of each area.
Everything is working correctly, except the sum-function: The layer with the squares has a combined population of little more than 80 million. But after the join the result has either 76 million or 84 million depending which kind of geometric predicate im using. But never the correct 80 million.
Both have the same CRS and I'm using QGIS 3.4.3 Madeira.