1. U.S. Department of the Interior U.S. Geological Survey NHD Generalization Production Implementation Ellen Finelli Draft 5/10/2010 NHD Generalization Production Implementation Ellen Finelli Draft 5/10/2010

2. Production Implementation Goals  Input: High Resolution NHD with Local Resolution content  Output: Cartographic 1:24K content with smoothed / simplified vertices  Test tools for National Map cartographic production implementation  Develop step by step procedures  Tool defaults or recommended tolerances  Including pre-processing (NHDPlus Build/Refresh)  Identify where additional development is required

3. NHD Generalization Development Cartographic Generalization Tools Developed by Larry Stanislawski Four Phases  Enrichment  Pruning  Smoothing  Validation

4. NHD Generalization Process Enrichment - Data Preparation  Create catchments for each networked feature  Calculate upstream drainage area (UDA) and catchment density (length / area) for each flowline feature.  Assign density partition  Cluster and dissolve based on catchment density

5. NHD Generalization Development Pruning – Content Reduction  Simple Prune – Prunes complete dataset to a user defined density parameter (Single Density Value)  Stratified Prune – Prunes each density partition to user defined density parameter (Multi Density Values)  Prune short tributaries **  Prune Waterbodies **  Refined network pruning ** (** Not evaluated at this time) (** Not evaluated at this time)

6. NHD Generalization Development Generalize – Vector Simplification or smoothing**  Not operational at this time. Barb Buttenfield’s generalization operation sequences have been tailored for five of six terrain/climate conditions, but have not been implemented in toolbox. These tools are currently scaled to convert high resolution NHD to a level of detail appropriate for 50K to 200K. Validation** (** Not evaluated at this time)

7. Sample Subbasin 05050001  Local Resolution updates for  050500010108  050500010305  FY10 Graphic Schedule VA & NC (Cell ID)  Park, NC, VA(18037)  Grassy Creek, NC, VA(18188)  Mouth of Wilson, VA, NC(30981)  Sparta West, NC,VA(41906)  Homogeneous Terrain, dendritic drainage pattern

8. Cartographic Generalization Terms:

9. Generalization – Enrichment  Expected Results – Assumption  Local Resolution data would be partitioned together consistently

12. Should NOT have been included in High Density Should have been included in High Density Partition

13. Generalization – Enrichment Results  Enrichment – Actual Results  Catchments were created successfully  Density Partitions created (5 partition classes)  Density Partitions clustered and dissolved (3 partitions)  Not all Local resolution data resulted in the dense partition  Some high resolution data resulted in the dense partition

14. Generalization - Pruning  Pruning - Expected Results - Assumptions (24K Scale Pruning)  Leave exiting 24K scale data as is  Prune local resolution data  Producing a consistent density across the subbasin.

17. Generalization Pruning Results  Pruning – Actual Results  Simple Network Prune (Single Density Value)  24K results not adequately pruned in local res area  Need to tweak the density value

20. Note: Features that should have not be pruned

21. Generalization Pruning Results  Pruning – Actual Results  Stratified Network Prune  24K results adequate  Recommend use of the following formula

22. Formula for Stratified Prune Formula for Stratified Prune - Density Partition Values for 24K USTopo Data Density (catchment area / stream length) Density Partition Original Density Values Suggested Stratified Prune Partition Density Values Sample Values @ 5% Low volume of High Resolution Data Low1aa0.57812 High Resolution DataMed2bb - x% *1.52421 Local Resolution Data in High Resolution Dataset High4cb1.60443 * Note: Specific Value recommended TBD (~ between 2% to 5%)

24. U.S. Department of the Interior U.S. Geological Survey

31. Results – workable for 1:24,000-Scale  Although the density partitions, were not as expected, the stratified prune produced results adequate for 24K scale representation, in this sample subbasin.  Test with additional sample datasets  Fully populated local resolution Subbasins  Use of previous generation original 24K NHD to determine density values

32. Moving Forward…  Issues for National Map and Users  Continue Testing with larger variety of subbasins  Incorporate the smoothing / simplify process  Consolidate enrichment tools  Provide NHD Generalization User Guide  Old technology (Coverages and AML’s)  Storage of NHD generalized data  Where will generalized NHD data by stored?  What are the access requirements?  Distribution of Tools  AK