Presents new evidence on New York City's low income population and three component groups--welfare recipients, eligible nonrecipients, and the near poor. With data from a survey of 18,000 city households and specially commissioned Census tabulations, the authors analyze the sizes and characteristics of each group in 1970, covering basic demographic descriptors, income sources, participation in the job market, and fitness for work. Among other topics on which there has been little or no statistically based evidence available previously, they examine welfare participation rates among eligibles and the distinguishing attributes of eligible nonrecipients. Their data reflect detailed welfare eligibility tests essentially similar to those in force at welfare centers at the time the data were collected. 270 pp. Ref.