U.S. Department of the Interior U.S. Geological Survey National Geospatial Technical Operations Center Carl Nelson 4/14/2009 Maintenance I and Maintenance II Carl Nelson 4/14/2009

Overview  History  Where we are  Where we are going

NHD Conflation Process  2002: USGS, USFS, States and Contractors began conflation of 100K to 24K (High Resolution) NHD  File types used to create NHD datasets  Digital Line Graph (DLG)  Cartographic Feature File (CFF)  Tagged Vector Hydro (TVH)  State 24k DLGs (i.e. New York, Wisconsin, Texas, etc)  2007: Conflation of nationwide High Resolution NHD (24K) geodatabase completed

Why Maintenance?  During conflation of 100K to 24K NHD  Editing tools were not available during the initial conflation 100K to 24K  Subbasins were edge-joined before they went in the GeoDatabase, but could not fix one already in the GeoDatabase  USFS contracted ESRI to develop edit tools  NHDEditTool  Maintenance begins

Maintenance Lite I  Resolve 1D Topology Errors  Feature to feature overlaps  Self intersecting features  Self overlapping features  Multi-part features  Resolve NHDMValue Errors (Measures)  Insure all reaches have measures  NHDFlowcheck now replaces NHDMValue

Maintenance Lite I  Run NHDFlowcheck  Regenerates geometric network  multi-part flowline features are automatically converted to single-part flowline features.  Checks for overlapping junctions  Checks for overlapping flowline features  NOTE: May also generate false positives for small pairs of flowline features connected to the same divergent and convergent junctions

Maintenance Lite I  NHDFlowcheck continued…  Node degree problems  Selects all flowline features that connected to a junction with multiple inflows and no outflows, or with multiple outflows and no inflows  Find network ends  Find non-traced flowline features  Traces all upstream features connected to selected network ends  Selects all untraced flowline features

Maintenance Lite I  Resolve Inter-CU connections  Resolve Gapped Names and Gapped or Branched Reaches  Gapped names connected where line work exists on 24k DRG  Resolve GNIS Name Errors (major names)  Main stems verified using GNIS shapefiles  Create XML Extract  Load XML Extract into copy of original data (XML2GDB) and re-run QA/QC checks

Maintenance Lite II  Resolve polygon (2d) topology errors  NHDArea overlaps NHDWaterbody  NHDArea overlaps NHDArea  NHDWaterbody overlaps NHDWaterbody  Check coastal subbasins for missing Sea/Oceans

Maintenance Lite II  Ensure all reaches have M_Values  Remove Branched GNIS Names  Check all WBAreaComIDs and correct or add as necessary  Check Coastlines (Coincident with 2d features) and correct as necessary

Maintenance Lite II  Split 2d stream/rivers and large waterbodies at subbasin boundaries  Insure that offshore islands have coastline  Create XML extract  Load XML Extract into copy of original data (XML2GDB) and re-run QA/QC checks

Questions or Comments?