R ggplot geom_tile without fill color

Question

I am trying to add a geom_tile layer to a plot without the filled color (just the outline). Is there a way to get a transparent tile where only the boundary is visible?

Thanks

Answer 1

If you only want the outlines as a single colour you can set fill = NA, and then set the na.value to NA

.data <- cbind( 
           expand.grid(x = 1:10, y = 1:10), z = runif(100))[sample(1:100,75), ]



ggplot(.data, aes(x = x, y = y)) + theme_bw() + 
   geom_tile(fill = NA, color = 'black', na.value = NA) 

Answer 2

I think you are after alpha parameter. Minimal example:

1. Create a plot with dummy data where you set color (for "boundary") and no fill:

   p <- ggplot(pp(20)[sample(20*20, size=200), ], aes(x = x, y = y, color = z))
   

2. Add geom_tile() with alpha set to zero:

   p <- geom_tile(alpha=0)
   

3. Add theme_bw() as transparent tiles look lame with a dark gray background :)

   p + theme_bw()