Combine coord_proj and geom_raster

Question

I am looking for a means of plotting raster data (using ggplot and geom_raster) on a small scale map. I would like to use ggalt and coord_proj to 'zoom-in' on particular regions of the shapefile, but I run into the error geom_raster only works with Cartesian coordinates

ggplot() +
    geom_polygon(data = land_df, aes(long, lat, group = group), fill = 'grey25')+
    geom_raster(data = df, aes(lon_bin, lat_bin, fill = sum_hours)) +
    coord_proj(xlim = c(-67, -63),ylim = c(0, 9))

Is there another simple means of generating zoomed in raster maps using coord_proj and avoiding this restriction that geom_raster only works with Cartesian coordinates?

The other options I can think of is to generate individual shapefiles for each 'zoomed-in' region, but I am plotting many of these rasters and would rather not have to generate individual shapefiles for each and instead use coord_proj to programmatically specify raster map limits.

Thanks

Answer 1

I think you need to use geom_tile() instead of geom_raster(). geom_raster() internally uses a rasterGrob, which is a bitmap that can only be scaled linearly. Hence the limitation to Cartesian coordinate systems. geom_tile() draws individual rectangles which can be transformed into any coordinate system.

I don't have your dataset, but I can show a very simple example:

df <- data.frame(x = 1:100) # a very simple dataset

p_raster <- ggplot(df, aes(x, fill = x, y = 0)) + 
  geom_raster() + 
  scale_fill_distiller()

p_raster

p_raster + coord_polar()
## Error: geom_raster only works with Cartesian coordinates

Now with geom_tile():

# for geom_tile(), map both fill and color to avoid drawing artifacts
p_tile <- ggplot(df, aes(x, color = x, fill = x, y = 0)) + 
  geom_tile() + 
  scale_fill_distiller() +
  scale_color_distiller()

p_tile

p_tile + coord_polar()