In 1889 the D. A. Sanborn Map Company, established roughly two decades earlier, absorbed Perris & Browne’s venture. Sanborn developed over 100 symbols to provide an even greater level of detail for insurers. This 1892 map illustrates several public improvements that spurred construction: Madison and Lexington Avenues have been opened, and Fourth Avenue has become Park Avenue, landscaped and lined with homes and other institutions.
The post–Civil War economic boom generated a period of active brownstone construction on the East Side, visible on the map as small, red rectangles. Larger red shapes line Fifth Avenue, which is beginning to host a procession of elite buildings. AR