Watershed Boundary Dataset HUC 4s

Retirement Notice: This item is in mature support as of April 2026 and will be retired in December 2027. A new version of this item is available for your use. Esri recommends updating your maps and apps to use the new version. Each drainage area is considered a Hydrologic Unit (HU) and is given a Hydrologic Unit Code (HUC) which serves as the unique identifier for the area. HUC 2s, 6s, 8s, 10s, & 12s, define the drainage Regions, Subregions, Basins, Subbasins, Watersheds and Subwatersheds, respectively, across the United States. Their boundaries are defined by hydrologic and topographic criteria that delineate an area of land upstream from a specific point on a river and are determined solely upon science based hydrologic principles, not favoring any administrative boundaries, special projects, or a particular program or agency. The Watershed Boundary Dataset is delineated and georeferenced to the USGS 1:24,000 scale topographic basemap. Hydrologic Units are delineated to nest in a multi-level, hierarchical drainage system with corresponding HUCs, so that as you move from small scale to large scale the HUC digits increase in increments of two. For example, the very largest HUCs have 2 digits, and thus are referred to as HUC 2s, and the very smallest HUCs have 12 digits, and thus are referred to as HUC 12s. Dataset Summary Phenomenon Mapped: Watersheds in the United States, as delineated by the Watershed Boundary Dataset (WBD) Geographic Extent: Contiguous United States, Alaska, Hawaii, Puerto Rico, Guam, US Virgin Islands, Northern Marianas Islands and American Samoa Projection: Web Mercator Update Frequency: Annual Visible Scale: Visible at all scales, however USGS recommends this dataset should not be used for scales of 1:24,000 or larger. Source: United States Geological Survey (WBD) Data Vintage: January 7, 2025 Questions? Please leave a comment below if you have a question about this layer, and we will get back to you as soon as possible.

停用通知：本项目自2026年4月起进入成熟支持阶段，并将于2027年12月正式停用。当前已有新版本可供使用，Esri建议您更新地图与应用以适配新版本。

每个流域均被视为水文单元（Hydrologic Unit，HU），并分配有水文单元代码（Hydrologic Unit Code，HUC）作为该流域的唯一标识符。美国境内的HUC 2、HUC 6、HUC 8、HUC 10与HUC 12分别对应流域大区、次大区、流域盆地、次流域盆地与小流域。其边界依据水文与地形标准划定，勾勒出某一河流特定点位上游的陆地区域，且完全基于科学水文原则确定，不偏向任何行政边界、专项项目或特定机构与项目。

本流域边界数据集（Watershed Boundary Dataset，WBD）以美国地质调查局（United States Geological Survey，USGS）1:24,000比例尺地形底图为基准进行矢量化与地理配准。水文单元采用多层级分级流域系统进行划分并匹配对应HUC代码，因此当比例尺从小变大时，HUC代码的位数以2位为增量递增。例如，最大尺度的HUC代码为2位，即HUC 2；最小尺度的HUC代码为12位，即HUC 12。

### 数据集摘要
#### 测绘对象：美国境内由流域边界数据集（WBD）划定的水体流域
#### 地理覆盖范围：美国本土、阿拉斯加、夏威夷、波多黎各、关岛、美属维尔京群岛、北马里亚纳群岛和美属萨摩亚
#### 投影坐标系：Web Mercator
#### 更新频率：年度更新
#### 可视比例尺：全比例尺下均可正常显示，但USGS建议本数据集不适用于1:24,000或更大比例尺的应用场景
#### 数据源：美国地质调查局（WBD）
#### 数据基准时间：2025年1月7日
#### 咨询渠道：如有关于本图层的疑问，请在下方留言，我们将尽快回复。