Plotting shapefiles on top of Google map tiles

Question

I have some shapefiles I want to plot over Google Maps tiles. What's the most efficient way to do this? One path might be to use the pkg RgoogleMaps, however, it is still unclear to me how to do this. I assume using PlotonStaticMap with some combination of reformatting the shapefile data

Answer 1

From the developer, it seems to work nicely.

shpFile <- system.file("shapes/sids.shp", package="maptools");
shp<-importShapefile(shpFile,projection="LL");
bb <- qbbox(lat = shp[,"Y"], lon = shp[,"X"]);
MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = "SIDS.jpg");
#compute regularized SID rate
sid <- 100*attr(shp, "PolyData")$SID74/(attr(shp, "PolyData")$BIR74+500)
b <- as.integer(cut(sid, quantile(sid, seq(0,1,length=8)) ));
b[is.na(b)] <- 1;
opal <- col2rgb(grey.colors(7), alpha=TRUE)/255; opal["alpha",] <- 0.2;
shp[,"col"] <- rgb(0.1,0.1,0.1,0.2);
for (i in 1:length(b)) shp[shp[,"PID"] == i,"col"] <- rgb(opal[1,b[i]],opal[2,b[i]],opal[3,b[i]],opal[4,b[i]]);
PlotPolysOnStaticMap(MyMap, shp, lwd=.5, col = shp[,"col"], add = F);