National Hydrographic Dataset update

National Hydrographic Dataset update

Client wanted to update the existing NHD dataset to match its current state after the year 2005 Natural disaster in Louisiana Coastal areas, USA.

Client

Client is an experienced provider of GIS services to support the long and short term needs of both public and private sectors in North America. They provide effective GIS solutions for water related and various mapping projects.

Challenge

Photo Revision imposed a big challenge to revise the existing data on a severely affected area. Adding new features and deletion of existing features of the data set needed careful interpretation. Nearly 99% of features were modified within the given area of interest. Preserving the existing attributes was a big challenge because changes of existing attributes will make the data set obsolete.

Solution

NHD shape files for the sub basin of interest were downloaded from USGS website and High resolution Images for the year 2005 were downloaded from State atlas website. Downloaded shape files were split based on the quadrangle boundaries in order to increase the speed of photo revision. Each feature in the dataset was carefully interpreted and modified based on the USGS standards. Automation techniques were used to preserve the existing attributes to avoid human blunder error. Refined methodologies were adapted to photo revise the dataset that ensures minimal topological errors in the final output. Different automation techniques were followed to remove the minimal topological errors in the final output. Finally individual quad shape files were edge matched to get the final photo revised NHD dataset for Louisiana.

Key Statistics

1. Photo Revised Over 41 quads, i.e. 6888 sq km of Louisiana, USA
2. Digitization Tool – ARCGIS 9.2, as per USGS mapping standard
3. Data capture includes 20 different attribute layers

Benefits

The NHD is a comprehensive set of digital spatial data that contains information about surface water features such as lakes, ponds, streams, rivers, springs and wells. Within the NHD, surface water features are combined to form “reaches,” which provide the framework for linking water-related data to the NHD surface water drainage network. These linkages enable the analysis and display of these water-related data in upstream and downstream order.