Problems maping data with ggplot2 and maps in R

0
votes

I am trying to plot gridded data and over this plot country boundaries. I get the boundaries form maps package. My code start like this:

graf <- ggplot(data=my_data,aes(x=lon,y=lat,z=med_pos,fill=med_pos))
graf <- graf +  + scale_fill_gradient2(low='blue',mid='green',high='red', na.value = 'black')
graf <- graf + geom_tile()

This function well and plot the data as "filled contour". When I try to put as polygon the countries boundaries my code crash. This is the way I do it:

map_data <- map_data('world2')
graf <- graf + geom_polygon(data=map_data,aes(x=long, y = lat, group = group),color='black',fill=NA)

But if I run this last piece alone, it works. Do someone know what is the problem ?

As bonus question, does anyone know how to settle in scale_fill_gradient min and max value ?

Note, my_data is a data.frame with 3 columns, lat , lon and med_pos. These have the coordinates and the value I want to plot.

1
rggplot2maps

1 Answers

0
votes

I have found the solution and problem. The problem is starting the graphic with inherit data. Width this code work:

graf <- ggplot() + geom_raster(data=my_data,aes(x=lon,y=lat,fill=med_pos)) 

graf <- graf + scale_fill_gradient2(low='blue',mid='green',high='red', na.value = 'black')

map_data <- map_data('world2')

graf <- graf + geom_polygon(data=map_data,aes(x=long, y = lat, group = group),color='black',fill=NA)