I have a program that creates a Png file using Rgooglemap with an extent (lonmin,lonmax,latmin,latmax) I also have a contour plot of the same location, same extent, same sized (height/width) png file. I'm looking for a way to make the contour semi transparent and overlay it on the google map ( hybrid map) Since I have 7000 of these to do an automated process is desired ( grin) Any pointers in the right direction ? [[alternative HTML version deleted]]