River deltas are formed when a river meets a larger body of water, such as an ocean or lake, and deposits its sediment. Over time, the sediment builds up and creates a landform that is typically triangular in shape. Major cities are often located on river deltas because they provide a natural transportation route for trade and commerce, as well as access to fresh water. Some examples of major cities located on river deltas include New Orleans, Louisiana (Mississippi River Delta), Shanghai, China (Yangtze River Delta), and Cairo, Egypt (Nile River Delta).