[GIS] How to get R to recognize a discrete raster layer

Question

I am trying to work with discrete data on land use in Australia. I load up the file as follows:

library(raster)

dat<-raster("C:\\Users\\Douglas\\Desktop\\GIS Project\\LandUse\\Land use of Australia 2005-2006 - National Map - ESRI GRID - integer - Geographics\\luav4g9abll07811a02egigeo___\\lu05v4ag\\hdr.adf")

Here is more information about the raster file:

class       : RasterLayer 
dimensions  : 3401, 4150, 14114150  (nrow, ncol, ncell)
resolution  : 0.01, 0.01  (x, y)
extent      : 112.505, 154.005, -44.005, -9.995  (xmin, xmax, ymin, ymax)
coord. ref. : +proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs 
data source : C:\Users\Douglas\Desktop\GIS Project\LandUse\Land use of Australia 2005-2006 - National Map - ESRI GRID - integer - Geographics\luav4g9abll07811a02egigeo___\lu05v4ag\hdr.adf 
names       : hdr 
values      : 1, 2329  (min, max)
attributes  :
         ID COUNT COMMODITIES                 COMMODITIES_DESC IRRIGATION                         IRRIGATION_DESC LU_CODE
 from:    1  3199          -1 Non-agricultural land or no data          0 Dryland agriculture, not ag. or no data     125
 to  : 2329     1          -1 Non-agricultural land or no data          0 Dryland agriculture, not ag. or no data     114
                               LU_DESC                    LU_DESC2                    LU_DESC3 T.CODE
 CONSERVATION AND NATURAL ENVIRONMENTS Managed resource protection Traditional indigenous uses  1.2.5
 CONSERVATION AND NATURAL ENVIRONMENTS         Nature conservation  Natural feature protection  1.1.4

and when I simply plot this map, it seems that R does not see the values as discrete, but rather continuous values.

plot(dat,"T.CODE")

How to get R to recognize the values as discrete and not continuous?

Answer 1

You can use levelplot from the rasterVis package to plot with categorical labels:

> r = raster(matrix(sample(1:3,25,TRUE),5,5))
> levels(r)=data.frame(ID=1:3, code=LETTERS[1:3])
> rasterVis::levelplot(r)

R uses the presence of a "RAT" (Raster Attribute Data) to define a raster as categorical - see help(ratify) for functions around this (my call of levels(r) in my example is calling raster::levels as documented in help(ratify).