Hi Kasey,
I tried doing a spatial join with MMQGIS in 2.18 and although at first it seemed it froze, after a few seconds it performed the sum operation just fine.
I usually run the Vector > Data Management Tools >Join Attributes by Location in QGIS 3 and so far I haven’t run into major issues. I am guessing your professor is right and the problem you are facing might be due to the data. It’s true that GIS software in general can be tricky when importing CSV files …I’m also currently banging my head trying to figure out how to do operations with a massive csv database, so I feel your pain.
I think you already tried this, but still, just to confirm, have you tried “Saving as” a shapefile and making sure that the layers were both in the same CRS? There is another thing you can try, it might work. Try using the field calculator to create a new column, choose any numeric format and just populate it using one of the fields that is giving you trouble (just type “NAME OF THE PROBLEMATIC FIELD” as the expression, including the quotation marks). Then try doing the spatial join and choose only that new field to do the sum and check if that works.
These issues are not exclusive to QGIS… I use both Arcmap and QGIS and alternate whenever either of them gives me trouble to do any operation. It’s not ideal but so far it has worked for me.
Let me know if this helped,
Best,
Javier
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