Tatami were originally a luxury item which graced the homes of the well-to-do when most people's floors were made of packed dirt.
There are various rules concerning the number and layout of tatami mats; an inauspicious layout can bring bad fortune. The mats must not be laid in a grid pattern, and in any layout there is never a point where the corners of three or four mats intersect.
In Japan, the size of a room is typically measured by the number of tatami. Shops were traditionally designed to be 5 1/2 mats, and tea rooms and tea houses are frequently 4 1/2 mats.
Tatami mats are associated with Japanese religious rites and the tea ceremony. Most modern Japanese homes still have at least one tatami room.