This layer is a geo-referenced raster image of the Army Map Service 1:250,000 scale topographic map of the Trigu Tsho (Tibet) region. This map (NH46-14) was compiled in 1954 from: best available medium scale maps; Eastern Asia, 1:1,000,000, AMS, Sheet NH-46, edition 1945 and was first printed in this series in May 1956.
A digital raster graphic (DRG) is a scanned image of a standard series topographic map, including all map collar information. The image inside the map neatline is geo-referenced to the surface of the earth and fit to the Universal Transverse Mercator projection. The horizontal positional accuracy and datum of the DRG matches closely with the accuracy and datum of the source map.
This map series of China (Series L500) was created and printed by the US Army Corps of Engineers Army Map Service (AMS) during the 1950s. The AMS was later known as the Defense Mapping Agency, which is now subsumed under NIMA. These maps are a contoured topographic map series based largely on the Survey of India. These color maps have contour intervals of 100 meters. Map sources used to create these maps include British Survey of India maps, Japanese civil survey and military maps; United States Air Force (USAF) and United States Hydrographic Office (USHO) charts and a variety of other source maps simply described as the "... best available large scale and medium scale maps of China." These maps are in English, with modified Wade-Giles romanized Chinese place and feature names, many names also appear as Chinese ideographs. These are typical topographic maps with all of the normal topographic information: contours, transportation, culture, etc. Please pay close attention to map collar information on projections, spheroid and keys to grid numbering and other numbers which appear inside the neatline.