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I have two layers, one polygon of output areas in the UK and a point layer of retail centers. I want to use select by location to find out how many output areas are within 1 km from a retail center. The select by location tool does not have the precision parameter to enter the 1km distance. Does anyone have any suggestion whether there's a plugin that does this? I've done this on ArcGIS but I want to know how it is processed in QGIS.

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    You can buffer 1 km, then use buffer in Select by Location. Another processing step though.. – BERA Oct 16 at 10:41
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The trick is to use the true distance between the point (in the CRS unit) instead of using a buffer, which is only an approximation.

One way to do the join is by using a virtual layer.

Go to the menu Layer > Add Layer > Add/Edit Virtual Layer... and enter the following query.

If you want to keep polygons without nearby points, replace join with left join

select pg.*, count(*) as count_nearby_rail_centers
FROM myPolygonLayer pg
   JOIN myPointLayer a
      ON ST_Distance(pg.geometry, b.geometry) <= 1000
group by pg.id
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If you switch the select tool to mode 'Select Features by Radius' you can enter a search radius.

enter image description here

If you don't want to do this manually, you can make a buffer on the points and do a select by location like @BERA also says.

BTW not sure if this is present in QGIS 3.10.3, but is in 3.14.16.

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