Microsector
A microsector is a part of a Grid Sector. Basically, it is aa square of 10 sims long and 10 sims wide. The term is unofficial and it was invented by Second Life Geography team to define places inside a grid sector.
Structure and naming
Since a grid sector is a square of 100/100 sims, a microsector is a square of 10/10 sims (2.56/2.56 km). That means that a grid sector is made of 100 microsectors (10/10) and that a microsector can host 100 sims (10/10 if it contains no void ocean). Since grid sectors are named like squares inside a chess board, the same system can be used also for microsectors. This allows us to name them by rows (from 1 to 10) and columns (from A to J). So, one grid sector is composed of 100 microsectors, named from A1 to J10. The same system can be used to designate sims inside a microsector.
Reason
The use of microsectors is needed for high-precision maps. It is needed as an alternative way to define coordinates and places inside a grid sector. Sometimes, a Microcontinent or a Sim Group are too small to be found easy on a map of a grid sector.