Calculating cumulative sum of area values in attribute table by graphics in QGIS

Question

In QGIS I have a set of polygons divided into plots, each polygon has a diameter and area. I would like to sum up the polygons per each plot area.

From the attribute table, the polygons are not distributed according to the plots but are randomly scattered across the plots.

How can I sum up the polygons per plot by selecting them on the map overlay per plot so as to have an area sum per plot?

Answer 1

Using the steps below you should be able to do that:

• Create a new attribute for your circle-like polygons (let's call it "Plot Number") in the attribute table.
• Use the "Select by Location" tool (Processing Toolbox -> Vector Selection, with the geometric predicate "are within") and then the Field Calculator in your Attribute Table (don't forget to tick "Only update n selected features" at the top) to give each circle-like polygon its Plot Number (for instance all circle-like polygons within Plot 1 will have "Plot 1" as the Plot Number attribute)
• Use "Dissolve" (Processing Toolbox -> Vector Geometry) with Plot Number as the "Dissolve field(s)" so that your circle-like polygons will be grouped by their Plot Number attribute.
• Now you can select all circle-like polygons by the plot they fall in and do all the calculations you want based on that.

Your final result should look something like the image below.