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I have a bunch of points on a map on a river that branches. I want an easy way to select one branch from the other and was hoping I could just somehow "grab" those points on the map and add a column to the attribute table with those points that would delineate the two branches.

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Frist of all make an attribute to every single branch; every single branch of the river must be a single polygon's layer feature.

by your question I think you need to do the following steps:

Step 1 Generate a buffer poligon of every branch Qgis~Menù -> Vector -> Geoprocessing Tool -> Buffer. Set "distance" value in a way that you are sure to cover the points around every branch.

Step 2 Use the new buffered polygon layer in a spatial join of the points to add specific attribute Qgis~Menù -> Vector -> Data Management Tools -> Join attribute by location

Set "Input Layer = yourPointsLayer " and set "Join layer = buffered-branch-layer ", use these (check on) geometric predicate: "intersect, touch, are within", select the field to add (for example the field generated on step 1).

NOTE: There are two important settings that are critical in the process

  • The buffer size (step 1) must be not too small or too big
  • The "join type" setting in spatial join (step 2)
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