Charles Gwathmey, an architect whose work transformed parts of Miami and New York, died of cancer in Manhattan on Monday. He was 71. He founded Gwathmey Siegel & Associates with Robert Siegel in 1968. He branched out into museum design in 1996, creating the Museum of Contemporary Art in North Miami with Miami architect Jose Gelabert-Navia. He designed many luxury homes in the East End of Long Island and also the Sculpture for Living, a luxury condominium that transformed the Astor Place area of New York’s East Village.