Topographic maps are maps that systematically portray the spatial relationship among both physical features, such as contour lines (lines of equal elevation) and hydrographic symbols, and cultural features, such as roads or administrative boundaries. Topographic maps are also known as “topo maps,” "quad sheets," and "Digital Raster Graphics (DRG)." In the United States, the USGS has been responsible for the creation of topographic maps since 1879.