Do you mean in terms of Blitz units? I usually use 1 blitz unit = 1 metre (useful because like, a 100th of a blitz unit = a centimetre, and 1000 blitz units = 1 kilometre - none of this crazy inches, feet, yards, and miles nonsense which can't be divided into an integer). Although you can do it however you want really. Don't go too small or you start getting entity clipping on the camera when you get close to things.
+BlackD
+BlackD