During the course of this research, a number of nineteenth-century buildings which are still standing in Mexico City were photographed and the following information noted: The number of stories, the number of additions to the original structure, and the use assigned to each addition at the time of the visit. At each building an individual was sought who might provide the following information: (1) The use which the interior parts of the building received; (2) the number of housing units in the building; and (3) the changes introduced in the building to accommodate new business, small stores, or private offices. Those elements of the building which might reveal the use and overall condition of the structure were photographed, and the following criteria were established for describing the general use which might be assigned to a given building: