Changing size of proportional dots in ggplot map

Question

I'm trying to create a proportional dot map using ggplot2 R package but I have a problem I would really appreciate help with. I would like to represent shapefile polygons with dots of equivalent size. I've attempted to use ggplot and more specifically geom_point to achieve this. I can get this function to display the dots correctly proportional to each other but their actual size is much smaller than that of the polygons (I'm afraid I was unable to post the figure to illustrate this).

In my code I've specified the size of the dots (and scale size) using the variable 'area' which is a column of polygon areas in km2. However, this produces dots that are too small and I've not managed to rescale them. Is there a way to specify the mapping units somewhere so the dots are plotted in correct size or can I somehow relate the size to the polygon areas as the plotting function understands them? Much appreciated!

My code:

p <- ggplot()
p <- p + geom_polygon( data=basins, aes(x=long, y=lat, group=group)) #polygons
p <- p + geom_point( data=data, aes(x=long, y=lat, size = area, color=as.character(PC1_class))) + scale_size_continuous(name="area") #dots
p

alexwhan alexwhan · Accepted Answer · 2013-07-04T00:58:26

Without your data it's hard to give a specific answer, but it's to do with the range argument of scale_size_continuous(). This sets the minimum and maximum sizes of the points in geom_point(). So if you change to:

scale_size_continuous(name="area", range = c(1,20))

Then your minimum size will be 1 and the maximum will be 20. You then then need to work out which values work for your data.

Changing size of proportional dots in ggplot map

1 Answers