Photo Data of Primary Interest 
In the present research, there were four photo data items of 
primary interest in analyzing residential subareas of several American 
cities, 
(1) The location of the area relative to three concentric circular 
zones with mid-point in the central business district. In a photographic 
study of Birmingham, Alabama, the zonal classification was obtained by 
plotting roughly circular ecological divisions on a photo-map of the 
city. These outlines were determined by noting ma jor breaks in land use, 
and referring to terrain features and transportation arteries. The 
inner-zone borders were identified by changes in building types, such 
as a merging commercial and warehouse area joining a transitional, lower- 
class residential district. For the most part, the inner-zone was in- 
cluded within a radius of one and a half miles from the mid-town point. 
Ihe middle-zone was drawn to contain most of the city's heavy industrial 
installations. It extended to the mountain ridges on the north and south 
and included the longer established, denser sections to the east and west, 
The outer-zone comprised more recent residential developments on the 
eastern and western edges of the eliptical-shaped city. This zone also 
included certain typical, inter-mixed "fringe" developments, 
(2) The description of the area in terms of internal and adjacent 
land usage. This photo data item was also divided into three categories, 
a breakdown intended for subarea classification according to a generalized 
consensus of "residential desirability", Thus, depending on certain 
objective evidence reflecting varying degrees of residential status 
ascription, each subarea could be classified as having generally "favorable", 
"neutral" or "unfavorablert attributes, These neighborhood descriptions 
were determined by noting street patterns, house and lot sizes, mixture 
Of land use, presence or absence of trees and sidewalks, and the age and 
quality of construction where such was evident. Account was also taken 
of the surrounding land useage, the presence or absence of industrial, 
commercial or railroad facilities assumed to influence residential 
desirability. 
(3) The prevalence of single-family homes, This photo data item, 
concerned with the proportion of all dwellings of the single-unit, 
detached type, was subjected to experimental accuracy tests comparing 
the photographic observations with data obtained by ground surveys, These 
tests required detailed interpretation and enumeration of all individual 
residences, However, in the later analytical phases, the residential 
subareas were simply labeled according to descriptive categories of 
prevalence of single-family homes, such as "high", "medium", "low", etc, 
(4) The density of housing in average numbers of dwellings per 
block, This item, also concerned with quantitative information on 
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