The facade of a building, while traditionally thought to be a representation, also has the possibility to be indexical. The plan, on the other hand, while clearly indexical also has iconic characteristics. Writing attempts to suggest that both the plan and the facade can be used as indices. In order to have a writing in this context one must first make a distinction between a resemblance and a representation. A representation always refers to something external, while a resemblance also refers to internal characteristics.
Representations rely on a traditional notion of memory that is linguistic and historical.
A resemblance can also be understood as a simulacrum that is not based on a visual relationship. In a sense the simulacrum is a representation without resemblance or the sign of a sign. Such a condition of sign becomes an index. In architecture when one draws the crossing of two lines, it produces a cross which is an obvious icon of point, centre, focus, etc. The repetition of this crossing produces a grid, which is no longer concerned with centre and focus but rather with surface, texture, etc.