Harold Mayer was a professor of geography at the University of Wisconsin-Milwaukee and one of the leading scholars in the field of urban geography in the Twentieth Century. He specialized in urban and transport geography of North America with a focus on New York, Chicago, Milwaukee, and British Columbia. During his academic career, Mayer created an extensive photographic collection that he used as an instructional tool in his teaching. In his photography, he documented the changes in urban landscape of North and Central America. He often returned to the same city to take a picture of the same sight over the course of several years. His collection, consisting of approximately 50,000 slides, was donated to the American Geographical Society Library by his wife, Florence Mayer.