The rephotographic method, with its rigorous demands for systematic return, exact replication of vantage point, angle of view, and lens choice, had emerged originally out of the need for scientific evidence of change over time in ecological niches. Vergara's use of the technique was not exclusive; indeed, Vergara made other pictures, including of residents and smaller details. Beginning with The New American Ghetto, Vergara increasingly interwove these photographs, along with quotes from outside writers, fragments of comments by citizen-dwellers in the cityscapes he developed, and his own writing.
The rephotographic method, which emphasizes systematic return, exact replication of vantage point, angle of view, and lens choice for scientific evidence of ecological change over time, was initially developed by Vergara to provide proof of change in ecological niches.  Vergara's work expanded beyond this initial purpose, incorporating other photographs, quotes from external sources, and citizen comments into his cityscapes.