Digital Elevation Model (DEM) from the Hydrologic Derivatives for Modeling and Analysis (HDMA) database -- Africa

This dataset contains the Digital Elevation Model (DEM) for Africa from the Hydrologic Derivatives for Modeling and Analysis (HDMA) database. The DEM data were developed and distributed by processing units. There are 19 processing units for Africa. The distribution files have the number of the processing unit appended to the end of the zip file name (e.g. af_dem_3_2.zip contains the DEM data for unit 3-2). The HDMA database provides comprehensive and consistent global coverage of raster and vector topographically derived layers, including raster layers of digital elevation model (DEM) data, flow direction, flow accumulation, slope, and compound topographic index (CTI); and vector layers of streams and catchment boundaries. The coverage of the data is global (-180º, 180º, -90º, 90º) with the underlying DEM being a hybrid of three datasets: HydroSHEDS (Hydrological data and maps based on SHuttle Elevation Derivatives at multiple Scales), Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010) and the Shuttle Radar Topography Mission (SRTM). For most of the globe south of 60º North, the raster resolution of the data is 3-arc-seconds, corresponding to the resolution of the SRTM. For the areas North of 60º, the resolution is 7.5-arc-seconds (the smallest resolution of the GMTED2010 dataset) except for Greenland, where the resolution is 30-arc-seconds. The streams and catchments are attributed with Pfafstetter codes, based on a hierarchical numbering system, that carry important topological information.

本数据集包含来自水文建模与分析导数数据库（Hydrologic Derivatives for Modeling and Analysis, HDMA）的非洲区域数字高程模型（Digital Elevation Model, DEM）数据。该DEM数据由处理单元开发并分发，非洲地区共设有19个处理单元。分发文件的压缩包名称末尾附有处理单元编号，例如`af_dem_3_2.zip`即包含3-2号处理单元的DEM数据。HDMA数据库提供了覆盖全球范围的完整一致的栅格与矢量地形衍生图层，其中包括数字高程模型（DEM）、流向、汇流累积量、坡度以及复合地形指数（Compound Topographic Index, CTI）栅格图层，以及水系与集水边界矢量图层。该数据覆盖全球范围（经度范围为-180°至180°，纬度范围为-90°至90°），其底层DEM数据由三套数据集融合而成：HydroSHEDS（多尺度航天飞机高程导数水文数据与地图）、全球多分辨率地形高程数据2010（Global Multi-resolution Terrain Elevation Data 2010, GMTED2010）以及航天飞机雷达地形测绘任务（Shuttle Radar Topography Mission, SRTM）。在北纬60°以南的全球大部分区域，数据栅格分辨率为3弧秒，与SRTM分辨率一致；北纬60°以北的区域（格陵兰岛除外）分辨率为7.5弧秒，即GMTED2010数据集的最低分辨率，而格陵兰岛的分辨率则为30弧秒。水系与集水区数据附带基于层级编号系统生成的普发夫施泰特编码（Pfafstetter codes），该编码承载了重要的拓扑信息。