Mega Basins (Feature Service)

Eight mega-drainage basins for Massachusetts, aggregated from the Major Basins layer. The delineations were based on the level 2 (4-digit) Hydrologic Unit Codes (HUCs) from the U.S. Geological Survey. Included are delineation of the Narragansett and Thames mega-basins. The HUC is a hierarchical, numeric code that uniquely identifies hydrologic units. Hydrologic units are subdivisions of watersheds nested from largest to smallest areas and are used to organize hydrologic data. In the 4-digit HUCs, the first two digits identify the region and the first four digits identify subregions. See full metadata Map service is also available.本数据集包含从主要流域图层聚合得到的马萨诸塞州8个大型汇水流域（mega-drainage basins）。本次流域划定工作基于美国地质调查局（U.S. Geological Survey）发布的二级（4位）水文单元代码（Hydrologic Unit Codes，HUCs）。数据集涵盖纳拉甘西特（Narragansett）与泰晤士（Thames）大型汇水流域的划定范围。HUC是一种层级化的数字编码，可唯一标识水文单元。水文单元是按面积从大到小嵌套划分的流域子单元，用于组织水文相关数据。在4位HUC编码体系中，前两位代码代表流域大区，前四位代码代表流域亚区。完整元数据可查阅，配套地图服务亦可供使用。