This dataset identifies areas with steep slopes in two categories used in local planning agencies: slopes 15-25% and slopes over 25% (slope=rise/run).
The dataset is intended for general planning purposes only, and may not be appropriate for site specific analysis.
Coordinate System: New York State Plane, FIPS zone: 3101 (Formerly East Zone 4801), Units: Feet, North American Datum 1983. This data can be accessed electronically on the Westchester County GIS web site http://giswww.westchestergov.com
148 Martine Avenue, Room 214
The source for this slope dataset was photogrammetic 5-foot interval elevation contours produced from 100-scale April-2000 aerial photography flown at an altitude of 4800 feet. (Step 1) The 5-foot contours were input to generate an elevation surface (grid) using the Topo-toRaster tool in ESRI ArcGIS software. Output cell size was set to 5 feet.
The elevation raster was input to generate a percent (%) slope raster using Spatial Analyst\Surface Analysis\Slope tool, again with output cell size set at 5 feet.
The Slope surface was input to generate slope contours (arcs) using Spatial Analyst\Surface Analysis\Contour, with contour interval set at 5 and Z factor set at 1.
From the slope contours, arcs with contour values of either 15 or 25 were selected and exported to a new file.
These arcs, defining the boundary between slope categories, were clipped to the county boundary to produce 'closed' arcs, for Step 6.
The closed arcs were converted to polygons using the feature to polygon tool.
Values were assigned to the slope polygons based on the slope raster using ArcToolbox\Conversion Tools\From Raster\Raster to Point tool, and performing a Spatial Join to the average value of all points inside each polygon.
Internal feature number.
Explicit definition of the coded value for slope category, either 15 to 25% (GRID_CODE = 2), or over 25% (GRID_CODE = 3)
Coded value of slope category, where 2 = 15 to 25% slope, and 3 = over 25% slope. Used for symbology and processing.
148 Martine Avenue Rm 214
Westchester County makes no warranty as to the accuracy or completeness of the county's GIS database, and will not be held responsible for any omissions or inaccuracies.
148 Martine Ave., Room 214