The set of LocalStations is called ls and the number (100) designates the cardinality of the set. All the block instances within a block set typically have the same relationship with its surroundings (given by the channels).
A block set is not an array, so the thirteenth block cannot be identified by e.g. ls(13). The number of elements in a block set is determined when the system is created, all blocks in the set are created as part of the creation of the system, blocks will be permanent part (instances) of the system instance, and sets of blocks cannot be created dynamically.