Upper Mississippi Region's NHDPlus Data Processed through VPU 07
The National Hydrography Dataset Plus Version 2 (NHDPlusV2) offers a systematic file structure designed to support hydrologic and spatial analyses. This data, distributed by the Environmental Protection Agency (EPA), is organized in a manner that allows users to easily subset data by region and processing unit.
### Regional Planning Units (RPUs) and Vector Processing Units (VPUs)
NHDPlusV2 data is geographically segmented into RPUs, which represent large regional delineations, often encompassing Hydrologic Unit Code (HUC) 8 watersheds. These RPUs are further subdivided into VPUs for vector data processing. Within each RPU or VPU folder, the data is organized by drainage areas or hydrologic units.
### Typical Directory Organization
The data is distributed across directories as follows:
``` NHDPlusV2/ │ ├── RPU_XX/ # Regional Planning Unit folders (e.g., RPU_01, RPU_02) │ ├── VPU_YY/ # Vector Processing Unit folders within each RPU │ │ ├── Catchment/ # Catchment polygons shapefiles │ │ ├── Flowline/ # Flowline (stream networks) shapefiles and attributes │ │ ├── Elevation/ # Optional elevation data grids │ │ ├── DrainageArea/ # Files related to drainage area delineations │ │ └── Attributes/ # Related attribute tables (DBF, CSV) │ └── Metadata/ # Metadata and documentation files for the RPU │ └── NationalFiles/ # Optional files at the national scale ```
### Key File Types and Formats
The NHDPlusV2 data includes several essential file types and formats, such as flowline shapefiles, catchment polygons, attribute tables, and optional raster data. These files are richly attributed, containing valuable hydrologic and landscape information.
### Attributes and Metadata
Each NHDPlusV2 data file is equipped with various attributes, including ReachCode, COMID, ArbolateSum, and more. Metadata files document data creation, update versions, and geographic extents per RPU/VPU.
### Purpose and Use
This organization enables users to subset data by region (RPU) and processing unit (VPU). It facilitates hydrologic modeling and analysis by providing interconnected flowline and catchment data within defined hydrologic boundaries.
For more detailed information, including recommended naming conventions, file descriptions, and attribute explanations, refer to the EPA's official NHDPlusV2 User Guide. The guide is available in pdf format and can be found on the EPA's website, with a size of 5.31 MB. The latest version, 2.1, was last updated on March 13, 2019.
It is worth noting that the EPA has a Free Viewers and Readers page to help users access and interpret the data.
Technology like data-and-cloud computing is essential for efficiently managing and accessing the NHDPlusV2dataset, as it allows users to easily subset data by region (RPUs) and processing unit (VPUs) in the cloud. This data-and-cloud computing technology has streamlined data organization, enabling hydrologic modeling and analysis in a manner that was previously impractical.
