URBAN COMMUNICATIONS SYSTEMS
A city is a complex living-system. Its anatomy and composition can be studied and analyzed like any other living system. Certain parts can be distinguished from the mass and identified so that eventually each microscopic element of the system can be assigned to a part. The interactions between these parts may then be traced over time. The parts themselves must be able to undergo at least one change of state so that it is possible to observe what happens to them in the course of time. The processes of birth, development, maturation, and decline may be described, and ultimately scientifically "explained," by the modifications within the parts and the patterns of interaction they exhibit.
However, a living system may be subdivided by many different methods, and independent observers find it difficult to agree as to which will ultimately yield the most information of a useful sort. This study of cities starts with those pieces or elements which yield the least amount of ambiguity and disagreement at the start --the names and addresses of individual humans and their organizations. It considers the transactions between these unitary elements, and especially the messages which make up an important share of the interaction within a complete transaction. Nevertheless even here there exists a basis for disagreement about what constitutes a unit, or a transaction between units, as much as 1% of the time in advanced, mechanized cities with a history of census-taking and record-keeping behind them, and perhaps as many as 10-20% of the instances in cities still in the throes of settlement and organization, such as those to be found in much of Africa. Such uncertainty sets the limits to comprehensive measures of urban activity. The origins, paths, contents, and destinations of a portion of the communications comprise the present data for the functioning of a city. The sampled flow of events affecting the social units in the city, large and small, should provide the most balanced source of basic information about urbanism.
It is no overstatement to assert that the people in urban areas are preoccupied with communications. A city encompasses many thousands or even millions, of persons. Each person engaging in such communications is observed to have one or two probable locations or addresses, occasionally even more. A person with more than one address employs one or more standard paths to connect them, but he also moves with some regularity along a small number of other paths at various intervals. Not infrequently he seems to be exploring because the movements are unprecedented for him but fit patterns employed for systematic search. Each person in the urban environment is continually bombarded by messages from other persons, and he in turn must spend some time emitting messages of his own. The origins and destinations of messages and movements are correlated to a high degree.
A comprehensive analysis of the interactions within an urban population could be conducted in a manner equivalent to that used by biologists in their studies of living systems were it not for the presence of shields that have been created to fend off messages. This shield is called privacy. The small groups clustered inside these screens from communications (homes) are known to exchange messages to which the