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 Feeling Cooperative? It's up to you. The NHD truly is a cooperative product. Active users of the data are expected to be contributors as well. As you work with the data, please track your additions and improvements so that you can send them back to become part of the NHD. We intend to begin accepting user-supplied updates to NHD data only after it has been through the flow validation process. The NHD has been designed to identify, accept, and track updates, but the policies and procedures to do this are not fully developed. We need NHD users to help us evolve policies and procedures that will be usable and beneficial to both updaters and the national database maintainers. Obviously, this dynamic process of growth must conform to certain conventions. The NHD has been designed with specific methods for adding, deleting, or correcting data. Some of these methods may be unfamiliar at first, but they are reasonably straightforward, and necessary to safeguard the integrity of the data for all users. Some changes can have significant impacts. Stream classification, for example, can affect natural resource management, flood hazard risk, development, storm water management, water rights, etc. It is essential that any changes made to the NHD are valid. Users expect the data to be valid, and the NHD is depending on users to help identify policies and procedures that assure reliability and validity as well as to add to and improve the data. These policies and procedures will take time to develop. In the meantime, we have developed initial procedures to accept updates to names. We can process updates to names, because names can be verified against an authoritative source, the Geographic Names Information System (GNIS). A special extract from GNIS is prepared that contains the name and associated GNIS_ID (among other items) for only hydrographic features. This extract is formatted into GIS coverages for updaters to validate names before they are submitted for incorporation into the NHD. Initially, the NHD will accept updates by receiving an entire NHD coverage of the updated area from the updater. The coverage should contain the updates, a list of the changed features (in the status table), and metadata that describes what was done to update the coverage. The central update software will extract the updates from the coverage using the status table, perform validation, and apply the changes to the NHD database. A long term maintenance objective is to simply receive transactions from updaters. But for now, whole coverages will be the method of exchanging updates. A tutorial is being developed that will provide step-by-step instructions on how to verify that the name and GNIS_ID are valid, how to edit the actual data, and how to build the 'status' table that will identify which feature was edited and the type of edits. It is difficult to estimate how quickly we will be able to respond because no one knows how many changes will be submitted. We also do not yet have the tools that will make it easier for a user to capture their changes during the normal course of working with the data. We hope to develop those in cooperation with the user community. When people actively use the data and discover shortcomings, this real world experience will help us develop the tools, policies, and procedures needed to maintain the NHD. |
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