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I am fairly new to QGIS. I am using version 3.18. The idea is to find the relationship between the project activities of NGOs in a country and the level of conflict. For this I have a txt delimited vector layer of all conflicts in a country. I also have a geocoded data of all project activities done in the country. In order to have a clear unit of analysis, I have created a layer with a 20km grid. To start with I overlay the grid vector and point layer (location of the conflict). enter image description here

I want to combine the attribute of both layers so that I can associate each conflict with the corresponding grid it falls into. I have been trying "Join attributes by location" but it doesn't show me anything - as in, the resulting attribute table has "null". I'm not able to figure out where the problem is.

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Take a look at this question and the answer provided Empty fields after joining attributes by location to join point to polygon layer it might be helpful. Also you can look at the link provided in the comment by @Taras https://docs.qgis.org/3.16/en/docs/user_manual/processing_algs/qgis/vectorgeneral.html#join-attributes-by-location-summary, provides information on performing JOINs.

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Whenever I get into this kind of situation I usually use spatial joins using spatial databases directly. This approach is learn and forget while using ever changing GUI isn't. If you have dynamic sources and some kind of integration you could use it to dynamically update maps. This approach is better when you have a lot of features. No matter which approach you use QGIS directly or spatial database, spatial index is usually a way to go.

For visualization purposes after spatial join I usually use QGIS.

https://postgis.net/workshops/postgis-intro/joins.html

One thing to notice, if you have multiple points inside a net you should decide which geo column is used in a new layer for visualization purposes.

or with spatialite, geopackage etc.

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