Starting with one given slot, users complete each composition by drawing in the remaining slots. The key is to make your slot blend into the surrounding completed slots while providing some material for the surrounding empty slots.
A user cannot draw a slot adjacent to one s/he has already drawn in order to ensure Big Picture remains a group activity. A slot cannot be drawn while an adjacent one is currently being drawn in order to ensure each slot blends with those around it.
Once a slot is chosen, users have two hours to complete it. Slots can be saved and returned to later, as long as it is still submitted within two hours.