You mean like the huge-ass ranches (called stations), some of which are bigger than some of the States in America?
There are, of course, a lot of areas that are pretty barren and won't sustain much in the way of livestock and/or plants, but they are basically equivalent to places like the badlands in the southwest of America.
The entire population of Oz is around 20 million, centered mostly around the coastal areas. Inland is mostly farming, and as I said, those farms tend to be rather huge, and don't really take all that many people to maintain.