Garrisons can be of three types although they can be more than one.
- Training garrision: A concentration of soldiers for the purpose of being trained. This may require specialist equipment, a lot of space (artillery or armour) or privacy (3 Para Mortar Platoon).
- Concentrations of troops in one particular area: Squaddies have to live somewhere and although there are some disadvantages to grouping them together (inter regiment skirmishes), concentrating them in one place means you can find most of them in a hurry
- A grouping of soldiers in a hostile area where their purpose is to maintain the peace or for their own defence from the locals: Insert your own joke about aldershot here.