This data set represents smoothed, 2-foot bare earth contours (isolines) for the Headwaters Exeter River unit. The data set was extracted from a regional elevation contour data set derived from the Coastal New Hampshire LiDAR collection (2011). Prior to contour generation, the regional LiDAR raster was "smoothed" using the ArcGIS "Focal Statistics" tool using a 3x3 circular neighborhood. The contours were generated using the ArcGIS "Contour" tool while applying a Z factor of 3.2802 to convert the elevation values from meters to feet. Once generated, contours less than 1 meter in length were deleted. The contours were further generalized using the "Smooth" function from within ArcMap with a maximum allowable offset of 0.1 meter.
These 2-foot contours were developed for visual use and comparison with other GIS data sets. The suitability for technical, scientific, or other finished cartographic purposes is unknown and should not be assumed.
A companion data set representing smoothed versions of the raw contours is also available for GRANIT, recommended for cartographic use only.
Maintenance_and_Update_Frequency: None planned
Theme_Keyword_Thesaurus: ISO 19115 Topic Categories
Place_Keyword: United States
Place_Keyword: New England
Place_Keyword: New Hampshire
Place_Keyword: Headwaters Exeter River
Use_Constraints: Please cite NH GRANIT.
Contact_Organization: Earth Systems Research Center
Microsoft Windows 7 Version 6.1 (Build 7601) Service Pack 1; Esri ArcGIS 10.1.1.3143
The critical attribute of this data is the contour elevation, the absolute accuracy of which has been affected by a number of processing steps. The original LiDAR elevation deliverables had a 2 meter or better nominal post spacing (2m GSD) and a a bare earth vertical accuracy of 15.0 centimeters RMSEz or better. Prior to contouring, the input raster was "smoothed" using a 3x3 circular neighborhood. The original elevation units of meters were converted to feet using a factor of 3.2808.
Attribute_Accuracy_Value: Floating point
Efforts were made to ensure that individual contour lines do not cross one another. The polyline topology rules "Must Not Ovelap", "Must Not Intersect", "Must Not Self-Overlap", and "Must Not Self-Intersect" were enforced to achieve this.
Contour line segments less than 1 meter in length have been deleted.
Originator: Complex Systems Research Center, University of New Hampshire
Ran the ArcGIS "Contour" tool using temp_LiDAR_DEM as the input raster and a Z factor of 3.2808 to produce 2-foot contours. A post processing step to remove short contours (length < 1 meter) was also performed.
Final processing included 1) selecting all contours (from within ArcMap) and running the Advanced Editing "Smooth" tool with a Maximum Allowable Offset of 0.1 meter, 2) applying the "Densify" tool using a max_deviation (offset) of 0.025 meters (this step was necessary to remove the Bezier arcs introduced by the "Smooth" routine - otherwise, it was not possible to clip the contours), 3) clipping the regional contour data set by HUC10, 4) applying the "Must Not Ovelap", "Must Not Intersect", "Must Not Self-Overlap", and "Must Not Self-Intersect" topolgy rules and fixing any errors, 5) projecting each HUC10 data set from UTM to NH State Plane feet, NAD83, and 6) clipping the HUC10 data sets by HUC12.
(The original plan was to distribute the data by HUC10, but the large file sizes (in excess of 500 GB) were considered too large for web distribution. Once this finding was discovered, it was more expedient
to re-clip from the HUC10 data sets.)