Vergara has been compared to Jacob Riis for his photographic documentation of American slums and decaying urban environments. Beginning in the 1980s, Vergara applied the technique of rephotography to a series of American cities, photographing the same buildings and neighborhoods from the exact vantage point at regular intervals over many years to capture changes over time. Trained as a sociologist with a specialty in urbanism, Vergara turned to his systematic documentation at a moment of urban decay, and he chose locales where that stress seemed highest: the housing projects of Chicago; the South Bronx of New York City; Camden, New Jersey; and Detroit, Michigan, among others.