Microsector
A microsector is a part of a Grid Sector. Basically, it is a square of 10/10 regions (or sims). The term is unofficial and it was invented by the Geography Of Second Life 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 sector 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.