Topography concerns the shape and character of the Earth's surface, and maps were among the first artifacts to record these observations. In modern mapping, a topographic map or topographic sheet is a type of map characterized by large-scale detail and quantitative representation of relief, usually using contour lines (connecting points of equal elevation), but historically using a variety of methods. Traditional definitions require a topographic map to show both natural and artificial features. A topographic survey is typically based upon systematic observation and published as a map series, made up of two or more map sheets that combine to form the whole map. A topographic map series uses a common specification that includes the range of cartographic symbols employed, as well as a standard geodetic framework that defines the map projection, coordinate system, ellipsoid and geodetic datum. Official topographic maps also adopt a national grid referencing system.