When archaeologists start digging into the soil, they do not yet know what they are digging. They name and enumerate every difference as a unit. Then, a feature number is given to each of them depending on its structural property, for instance, whether it is a floor, or a brick or an oven. Progressively, a spacenumber is given to these features according to their restricted area such as a midden, etc. If these spaces are connected, they are categorized with respect to buildings. Then, these spaces or buildings are separated top to bottom as levels according to their historical sequence.
Suppose you are digging an area that has been abandoned and covered with dirt through the years. At first, you see very different traces in the soil, and you classify them into units. Then you find a coffee table and you give it a feature number. This feature, at the same time, includes everything that you previously enumerated as a unit. You go on, and with the new findings such as a couch and a TV, you understand that this is a living room that is defining the area. You enumerate this room as space. With everything you have found up until now, it is possible to say that this is a living room. At last, when you find the house by digging every threshold and beyond, you give it a building number that includes all the other parts