Supergrid can be understood as the most integrated lines constituting the main urban structure, or a part of the overall grid of the city which acts as a facilitator of longer range movement.
Hillier, B. (1996, 2007), Space is the Machine: A Configurational Theory of Architecture. Space Syntax: London, UK. pp.130; Read, S. (2005), Flat City: A Space Syntax Derived Urban Movement Network Model. In: Proceedings of 5th Space Syntax SYmposium, 341-357. pp343.