50' Contour Lines - Graham County

This dataset represents 50 foot contour intervals for Graham County, Arizona. The data were created by processing hillshade TIF files derived from the U.S. Geological Survey National Elevation Dataset. The processing produced ESRI formatted coverages for each county or part of a county. The U.S. Geological Survey has developed a National Elevation Dataset (NED). The NED is a seamless mosaic of best-available elevation data. The 7.5-minute elevation data for the conterminous United States are the primary initial source data. In addition to the availability of complete 7.5-minute data, efficient processing methods were developed to filter production artifacts in the existing data, convert to the NAD83 datum, edge-match, and fill slivers of missing data at quadrangle seams. One of the effects of the NED processing steps is a much-improved base of elevation data for calculating slope and hydrologic derivatives. The specifications for the NED 1 arc second and 1/3 arc second data are - Geographic coordinate system, Horizontal datum of NAD83, except for AK which is NAD27, Vertical datum of NAVD88, except for AK which is NAVD29, Z units of meters.本数据集涵盖亚利桑那州格雷厄姆县的50英尺等高距数据。本数据集的生成基于对源自美国地质调查局（U.S. Geological Survey, USGS）国家高程数据集（National Elevation Dataset, NED）的山体阴影TIF文件的处理。该处理流程为每个县或县的部分区域生成了ESRI格式的Coverage（覆盖要素集）。美国地质调查局已研发国家高程数据集（NED），该数据集是现有最优高程数据的无缝镶嵌成果。美国本土的7.5弧分高程数据是其核心初始源数据。除完整覆盖7.5弧分分辨率数据外，研发团队还开发了高效处理流程，可过滤现有数据中的生产伪影、将坐标系转换至NAD83大地基准、完成边缘匹配，并填补图幅接缝处的缺失数据缝隙。NED的处理流程带来的一项核心优势，是为坡度与水文派生参数的计算提供了更为精准完善的高程数据基础。NED 1弧秒与1/3弧秒数据的技术规格如下：采用地理坐标系，水平大地基准为NAD83（阿拉斯加州除外，采用NAD27基准），垂直大地基准为NAVD88（阿拉斯加州除外，采用NAVD29基准），Z轴单位为米。