I have a map of the UK imported as a raster. It was originally a JPEG and has areas that are coloured red and purple. I have a data set imported from a CSV file showing UK locations as dots. I want to select the dots that are within the coloured areas of the raster map.
I thought that in order to do this, I would need to create a new layer only containing the parts of the map that are red and purple and then use this to clip the other layer. I don't know how to just select these areas of the map without just doing it visually using a polygon (this would take ages, as there is so much detail!). Is there a way to select features by their colour?