Summary

Description

The USGS Shaded Relief Large service from The National Map (TNM) was created from the National Elevation Dataset (NED), a seamless dataset of best available raster elevation data for the conterminous United States, Alaska, Hawaii, and Territorial Islands of the US. Derived from the NED using a hill shade technique, this base map represents a continental view showing shaded relief from USGS NED layers at resolutions of 1/3-, 1-, and 2-arc-second (in Alaska only). This hillshade is actually five separate shaded relief datasets created from the original terrain data. Each shaded relief has different azimuths and altitude values as follows: 0 45, 135 60, 270 45, 315 45, 45 45. These five datasets are then combined into one feature class using map algebra to compute the raster layers using the following equation (shadedrelief1 + shadedrelief2 + shadedrelief3 + (shadedrelief4 x 2) + shaded relief5 / 6). This equation gives double importance to the 315 degrees azimuth and 45 degrees altitude. Color characteristics are the result of applying a color ramp in which RGB values range from near-white (RGB: 255, 255, 252) to brown (RGB: 156, 142, 107). The color ramp was applied with a stretch type of 4.3 standard deviations, since the scale of brightness values range from 130 to 1240. Contrast (24 percent) and brightness (3 percent) enhancements were applied for cartographic purposes. For additional information on the NED, go to http://ned.usgs.gov.