R - Australian Digital Elevation Model

#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)

#Area Of Interest (Doesn't Seem To Corespond To LAT LONG ?)
aoi <- extent(c(xmin = 165, xmax = 179, ymin = -47.85, ymax = -33)) 

#Use aoi as reference to crop the hill shade raster
hill.aus2 <- crop(x = hill.aus, y = aoi)

## Same for the elevations
alt.aus2 <- crop(x = alt.aus, y = aoi)

## Colour palette for the DEM
library(RColorBrewer)
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"))
aus.dem

## Add North arrow
north2(ggp = aus.dem, x = 0.72, y = 0.875, symbol = 1)