This is one of those hard problems to Google since I don't know the right words to Google! I have a list of 6,000 retail locations in the US, and I want to know, for any given point, how far away one is from one of them.
I assumed this was a "proximity map," but that seems to mean a few different things. I THINK what I want is something like this McDonald's map from Reddit, but with an infinity decaying radius so that, even in large states where there are no locations, one gets a sense for the distance.
It seems to me there are two strategies:
Take the 6,000 points and run a sort of nearest neighbor algo that shows the radius expand from the nearest location, across the whole country.
Take a map of the country divided into the smallest possible intervals -- Census tracts or something -- and, for each tract, find the distance to the nearest location. This makes less computational sense, but I'm vague on how the first strategy would work.
In any event, I obviously didn't invent this concept, so if there's a name for it, I'm sure I can find a good QGIS tutorial!