50' Contour Lines - Pima County

This dataset represents 50 foot contour intervals for Pima 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.本数据集涵盖美国亚利桑那州皮马县（Pima County）的50英尺等高距地形数据。该数据集通过处理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）的晕渲TIF文件生成。本次处理为每个县或县内分区生成了ESRI格式覆盖数据集（coverage）。美国地质调查局已构建国家高程数据集（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分幅高程数据是其核心初始源数据。除完整的7.5分幅数据外，研发团队还开发了高效处理流程，用于过滤现有数据中的生产伪影、转换至NAD83基准面、进行边缘匹配，并填补图幅接缝处的缺失数据缝隙。NED的处理流程带来了一项显著优化：用于计算坡度与水文衍生参数的高程数据基底质量得到大幅提升。NED 1角秒（arc second）与1/3角秒数据的规范如下：采用地理坐标系，水平基准面为NAD83（阿拉斯加州除外，采用NAD27），垂直基准面为NAVD88（阿拉斯加州除外，采用NAVD29），高程单位为米。