Not quite right, I'm 'fraid.
From Carl's site, section "About Us":
quote:
From the beginning, "micro layouts" have been defined as "small model railroads, usually less than three or four square feet in area, that nonetheless have a clear purpose and excellent operating capability."
The prescribed layout size is more a state of mind than a rigid dimension, although "four square feet or less" ("under 3600 square centimeters") has become the canonical size for a micro, regardless of scale. What distinguishes these layouts from simple dioramas is the requirement for "excellent operating capability". These are working railroads, not just display scenes or tail-chaser loops.
unquote
However, as he said himself, Carl didn't stick stiffly to this definition: "... more a state of mind than a rigid dimension...", which is too often overlooked, imho.
Regards
Armin