Shorelines:Humans use the boundary between water and land to define sea level, but shorelines are dynamic, migrating inland or retreating out through time as sea level rises and falls. Shorelines can also change with variations in sediment supply. Shorelines are not straight, they wind as they follow contours, streams and inlets. Remnants of past shorelines teach us about past sea level. In this map shorelines are shown as thick black outlines along the edge of the land. Zoom in to explore present shorelines touching to locate land elevations above and below shoreline (sea level).