Tech & Sources
GDAL, PostgreSQL/PostGIS, MapServer, Apache
Data Sources (one or more):
U.S. Geological Survey (USGS), U.S. Forest Service (USFS), National Elevation Data (NED), National Land Cover Data(NLCD), National Hydrography Data (NHD), Tiger/Line Census, 3D Elevation Program (3DEP), Geographic Names Information Service (GNIS), Open Street Map (OSM), Protected Areas Database v2.1 (PAD), National Interagency Fire Center (NIFC), National Weather Service (NWS), NASA, NOAA, National Wildfire Coordinating Group (NWCG), AirNOW.gov, U.S. Department of Interior (DOI), National Digital Forecast Database (NDFD), European Space Agency (ESA), USAFacts.org, ESRI, Google, Continental Divide Trail Coalition, Appalachian Trail Conservancy (ATC), National Snow and Ice Data Center (NSIDC), PRISM Climate Data Oregon State University, et al, and data collected in the field (trail trace)
Image: Viewshed, locations on trail where Mt. Shasta is visible.
Using NED rasters and gdal_viewshed create a raster view shed of the Mt. Shasta area. Next, do an intersection of that raster and trail vector data resulting in relevant trail geometry.
Interactive map using WMTS: