I am plotting points on a graph with ggplot and geom_point. The size of the dots corresponds to the magnitude of the data point. The magnitude goes from 2 to 10. I would like to draw the dots by applying a factor of 0.5 to their magnitude so that the sizes go from 1 to 5. In the legend, on the side of the graph, I would like to show the real magnitude from 2 to 10.
How can I do that?