for functions of the form w = f(x,y,z) it takes three dimensions for the domain and would require a 4th dimension for the range which humans can't do.
One way of thinking of this is think of f(x,y,z) as the temperature at any point in 3 space. In your case the temp is -1 everywhere.
You can't visualuze temperature in your 3 -D world can you human?
Actually you can if you add color as with infrared imaging