R - Elevation Map

#----Australian Elevation  Map----#

#Download Elevation Data (Ensure Working Directory Set)
alt.aus <- getData(name = "alt", country = "AU") 

#Calculating Slope & Aspects
terr.aus <- terrain(x = alt.aus[[1]], opt = c("slope", "aspect"))

#Computing Hill Shade From Aspect & Slope
hill.aus <- hillShade(slope = terr.aus$slope, aspect = terr.aus$aspect)

#Printing Digital Elevation Model
RdYlBu <- colorRampPalette(colors = rev(brewer.pal(n = 11, "RdYlBu")))

aus.dem <- ggR(hill.aus) + ggR(alt.aus, geom_raster = T, ggLayer = T, alpha = 0.75, 
                               ggObj = T) + 
  scale_fill_gradientn(colours = c("red", "orange", "yellow", "white"), name = "Elevation", 
                       na.value = "transparent", limits = c(0, 3000), 
                       expand = c(0, 0), 
                       guide = guide_colourbar(nbin = 2000, barwidth = 0.5, 
                                               barheight = 3, 
                                               title.theme = element_text(size = 7), 
                                               label.theme = element_text(size = 6.5), 
                                               draw.ulim = F)) + 
  coord_quickmap() + theme_map() + 
  theme(legend.position = c(0.9, 0.4), 
        legend.background = element_rect(fill = "transparent"))

#----The Four Panels----#
#Start PDF Function
pdf("australian_maps.pdf", width=15, height=12)

#Adding North arrow
map_arrow <- north2(ggp = aus.dem, x = 0.72, y = 0.875, symbol = 1)

#Displaying The Two Maps
ggarrange(bound_map, aus.dem, ncol=2, nrow=1)

#Exporting Plot Canvas To PDF.
dev.off()