New York City landmarks (NYCL) can be categorized into one of several groups: individual (exterior), interior, and scenic landmarks.[56] The National Register of Historic Places (NRHP) is the United States federal government's official list of districts, sites, buildings, structures and objects deemed worthy of preservation for their historical significance.[57] The National Historic Landmark (NHL) focuses on places of significance in American history, architecture, engineering, or culture; all NHL sites are also on the NRHP.[58] World Heritage Sites are designated by UNESCO as having cultural, historical, scientific or other form of significance, and are legally protected by international treaties.[59]