RIDGE FEATURE PROTECTION

Data Name: RIDGE FEATURE PROTECTION

Summary Statement:

This metadata summary applies exclusively to the data as it appears in this Loudoun County intranet/internet mapping application.

Summary:

The Ridgeline Protection Areas were developed to support the Mountainside Development Overlay District components of the zoning overlay district. Ridgelines are defined as contiguous critical elevation areas within the mapped MDOD, except where geographic or natural features, such as a water resource, saddle, gap, or manmade features existing prior to December 13, 2023, such as roads, form breaks in the ridge.

Description:

The Ridge Features layer is developed using readily available elevation data and the Geomorphon Landforms geoprocessing tool available thru Esri ArcGIS Pro software. The Geomorphon Landforms tool is based on a powerful algorithm that combines elevation differences and visibility concepts to classify terrain into landform types. A geomorphon is a representation of landscape based on elevation differences within the surrounding area of a target cell.

Tool parameters were chosen to provide a general representation of the primary and prominent ridge features. [Flat Angle Threshold = 3 degrees, Search Distance = 2,640 feet (1/2 mile), and Skip Distance = 660 feet (1/8 mile)]

From the resulting geomorphon dataset, the “PEAK”, “RIDGE” and “SHOULDER” classifications were combined to create the Ridge Features Layer.

Features may have been eliminated or generalized due to scale and intended use. To assist Loudoun County, Virginia in the maintenance of the data, please provide any information concerning discovered errors, omissions, or other discrepancies found in the data.

• All features outside of the existing MDOD limits were removed.

• All features within the MDOD but below the critical elevation defined within the MDOD were removed.

• All features less than 20 acres in size, not contiguous with the County Boundary, were removed.

• All features not contiguous with primary ridge MOD features were removed.

• All features contiguous with the primary ridge MOD feature but 400 ft or more in elevation below the primary ridge were removed.

The source data for the processing was:

Digital Elevation Model/DEM (~ 10 m cell size); USGS 1/3 Arc Second; 3D Elevation Program (3DEP) seamless products is 1/3 Arc Second resolution. 3DEP data serve as the elevation layer of The National Map, and provide basic elevation information for Earth science studies and mapping applications in the United States. Scientists and resource managers use 3DEP data for global change research, hydrologic modeling, resource monitoring, mapping and visualization, and many other applications. 3DEP data compose an elevation dataset that consists of seamless layers and a high resolution layer. Each of these layers consists of the best available raster elevation data of the conterminous United States, Alaska, Hawaii, territorial islands, Mexico and Canada.

Data are stored in the corporate ArcSDE Geodatabase as a line feature class. The coordinate system is Virginia State Plane (North), Zone 4501, datum NAD83 HARN.

Use Limitation:

The ridge features were derived through a modeling process based on elevation data. Currently no national standard for this type of process exists. The ridge features were generated using the best available data for Loudoun County and should only be used as a reference.

These data were generated for use by Loudoun County and are available to the public. These data are intended for use at 1:2400 scale or smaller. Acknowledgement of Loudoun County would be appreciated in products derived from this data.

Loudoun County GIS Disclaimer: https://logis.loudoun.gov/loudoun/disclaimer.html

Credits:

Data Owner(s): Department of Planning and Zoning & Department of Building and Development

General GIS Contact: Loudoun County Office of Mapping and Geographic Information, mapping@loudoung.gov