Almost all of SoHo is included in the SoHo-Cast Iron Historic District, which was designated by the New York City Landmarks Preservation Commission in 1973, and extended in 2010, and was listed on the National Register of Historic Places and declared a National Historic Landmark in 1978. It consists of 26 blocks and approximately 500 buildings, many of them incorporating cast iron architectural elements.   (wikipedia)

Another distinguishing characteristic of SoHo is the setted streets, not to be confused with cobblestone streets. Cobblestones are distinct because of their naturally-formed, inconsistent shape. However, setts are quarried and cut into rectangular and square shapes.