From "Elementary, Dear Data" they said this In episode "A Fistful of Datas" there was a point in the episode where Troi, Worf, and Alexander were all separated: Alexander held captive by the data look alike, Troi in jail guarding the prisoner, Worf talking to the people of the town while looking for Alexander. This would mean that the holodeck was supplying the illusion of depth to at least 3 people here. I figure the holodeck allocates so much space to each person and gives each user a set of walls with the illusion of depth on them. But there is only so much physical space on the holodeck. Wouldn't you expect an error to occur when too many people are on the holodeck due to lack of physical space on the holodeck?