I am trying to overlay a nominal variable (2 categories - rainfed vs irrigated) in a choropleth map over a numeric variable.
In order to highlight the difference in pattern among the two categories, I have outlined one category with a different color (irrigated areas in "red"), while the uncoloured ones are rainfed areas.
However, the map feels cluttered and the outline mixes with darker shades of the numeric variable.
I am trying to avoid using two different color shading schemes to represent the two categories as I feel that would hide the overall distribution of the underlying variable.
Is there a better way to represent this bivariate classification using the ggplots2 package in R (which I am currently using it for making the attached map)?
These maps are eventually going to be printed on paper.