These contour lines, created by the United States Geological Survey (USGS), are hydro-enforced to facilitate improved integration between hypsography and hydrography and are attributed with elevation, contour type, and contour interval. Contour intervals vary by location ranging between 5 and 100 feet.
The Shuttle Radar Topography Mission (SRTM) collected elevation data on a near-global scale to generate the one of the most complete high-resolution digital topographic database of Earth. As a digital elevation model (DEM), SRTM is an excellent resource for creating hillshades (shaded relief) and contour maps. SRTM is available at two resolutions: 1-arc second (approximately 30 meters) and 3-arc seconds (approximately 90 meters).
Available for the continental United States at a resolution of 1/3 arc-second (approximately 10 meters), the National Elevation Dataset (NED) is a seamless raster product derived from a variety of data sources and processed to create a uniform and consistent product.
Available for the United States, these digital versions of the USGS’s popular topographic maps depict surface elevation through the use contour lines. In addition to elevation, topo maps also portray a variety of both natural and manmade features. Topo maps are available at a variety of scales including 1:250,000, 1:100,000, and the popular 1:24,000 scale (7.5 minute).