50' Contour Lines - Maricopa County

This dataset represents 50 foot contour intervals for Maricopa 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马里科帕县（Maricopa County）的50英尺等高距数据。其制作流程为：先提取源自美国地质调查局（U.S. Geological Survey）国家高程数据集的地形晕渲TIF文件，再对其进行处理，最终生成适配各县级行政单元或其辖区分片的ESRI格式地理覆盖数据集。美国地质调查局已研发出国家高程数据集（National Elevation Dataset，NED），该数据集是当前最优高程数据的无缝镶嵌成果，美国本土的7.5角分高程数据为其核心初始源数据。除完整的7.5角分数据外，研发团队还开发了高效处理流程，可实现以下操作：滤除现有数据中的生产伪影、将数据转换至北美大地基准1983（NAD83）、执行边缘匹配，以及填补图幅接缝处缺失的狭长数据缝隙。国家高程数据集的处理流程带来的显著优势之一，是为坡度与水文衍生参数的计算提供了大幅优化的高程数据基础。NED 1角秒与1/3角秒数据的技术规范如下：采用地理坐标系，水平基准为北美大地基准1983（NAD83，阿拉斯加州AK除外，其水平基准为NAD27），垂直基准为北美垂直基准1988（NAVD88，阿拉斯加州AK除外，其垂直基准为NAVD29），高程单位为米。