Each route is an explicit traversal of retained primary mapping data. The interpretation stays separate from the measurements.
1. Route geometry
Coordinates are longitude, latitude in decimal degrees (WGS 84 output requested from the source services). The builder selects exact UGRC or NPS object IDs, orients each leg, and requires adjacent endpoints to agree within 0.02 metres. It does not run an unconstrained shortest-path search. Original vertices are retained. Consecutive duplicates within 1 mm are discarded. NPS records with social/non-public notes are excluded.
Hat Shop and Mossy Cave use documented NPS points to locate a turnaround on an existing mapped segment. The nearest point is interpolated along that segment; no line is drawn across the remaining offset to the point. A 10 m maximum offset is required. The actual offset, NPS point role and original source properties are saved in the route packet.
2. Distance and traversal
Distance is the sum of great-circle distances on the source vertices using mean Earth radius 6,371,008.8 m. The spherical approximation is separate from the source’s unknown positional accuracy. ArcGIS Web Mercator Shape__Length is not used. The calculation is horizontal path length, not slope distance. A round trip includes the outward path and one reversed return, without duplicating the turnaround vertex. Loop stems and spur detours are explicitly traversed twice.
The viewer’s progress, profile, map and 3D markers use this common cumulative distance. Visual map markers interpolate the original source vertices, so a sparse elevation sample cannot jump across a switchback. Clicks on retraced paths choose the occurrence closest to the current progress; use the profile or slider to distinguish outbound from return.
3. Terrain and elevation
The source is one retained 10 m, bilinear USGS 3DEP bare-earth export in NAD83 / UTM zone 12N (EPSG:26912). The vertical reference follows the conterminous-US 3DEP NAVD88 metre convention. The service is a mosaic of source dates and resolutions; its publication date is not a ground survey date. The existing copied display textures are radially warped and do not cover the southern Riggs Spring route, so they were not used to infer uniform-resolution trail profiles.
The full mapped itinerary is sampled at evenly spaced distances of 25 m or less. Out-and-back sample counts are even so the turnaround is included. Heights come from bilinear interpolation between DEM pixel centres. A centred mean of three samples smooths the profile. Open endpoints are kept; a closed loop wraps its neighbours. Ascent sums positive differences in the smoothed profile, and descent sums negative differences.
Both raw ascent and a second calculation at intervals of 50 m or less are retained as sensitivity checks. They are not uncertainty bounds. Unknown positional error beside steep walls can yield large vertical errors. A ground grid cannot recover tunnels, bridge decks, arch undersides or the walking tread. National aggregate DEM accuracy is not a measured local route-error bound.
Map shading is computed from the same DEM. Each interactive terrain crop is a 145 × 145 grid resampled from it, with 1× vertical scale. Cut sides only show the crop boundary; they are not strata. Route overlays stay visible over the surface. The elevation profile has a separate vertical plotting scale with absolute elevations labelled.
4. NPS figures and disagreements
NPS published miles, kilometres and climbing figures are retained independently. They are not used to stretch source geometry or rescale the profile. Some NPS pages have conflicting unit conversions, different variants or rounded totals; each affected route names the discrepancy. Older compiled lines may generalize bends and use different endpoints. The current evidence cannot uniquely assign the cause of every mismatch.
5. Stop meanings and reuse
A documented-point stop is the nearest route position to a named NPS point; the point’s original location, role and offset are retained. An editorial reading cue lies on a specified source segment but is not a surveyed viewpoint. Neither guarantees a view, a tree, an open trail or a safe stopping place.
UGRC, WFRC route data are licensed CC BY 4.0. BCC assembled, reversed and sometimes clipped the selected lines. NPS and USGS federal data retain their source disclaimers. No third-party photographs, Google imagery, proprietary undocumented tracks or ground-level scans are included. Read the complete credits and terms.