Remotely Sensed Data
Designated Public Hiking Trails

By Robert Bennett, Pickatrail.com

Many of the hiking trails depicted in Google Maps do not exist, or they are inaccurately depicted and/or incorrectly labeled. This document explains why using remotely sensed data to interpret designated public hiking trails without ground-truthing may be responsible for these errors and inaccuracies.

Google Remote Sensing - Figure 1

In the above Google map, five trail segments are depicted that join at a single location in Grand Canyon National Park. Four of the trail segments are labeled using incorrect names. One of the trails does not exist; the trail never existed. If Google had ground-truthed the data then a field analyst would have seen the four-way intersection in the photograph below. Not only are there only four trail segments at this junction, NPS (National Park Service) went out of its way to keep pedestrians on these four trails by placing large rocks along their borders. Notice the signpost in the photograph. On the other side of this signpost, the trails are correctly labeled. If Google had ground-truthed the data, a field analyst would have noted the correct trail names and the four trail segments at the junction.

Grand Canyon Trail Intersection - Figure 2

I hiked these trails; signposts identify the names of the trails and each trail has a unique name. Some of these trails had a ribbon-cutting ceremony. The names on the signposts match the names of the trails published in the news articles that document the ribbon-cutting ceremonies.

Interpreting trails from remotely sensed data without ground-truthing can sometimes result in erroneous and inaccurate polylines, in particular when the trail is covered by a forest canopy and/or located in a canyon or ravine, or when the trail is not visible and/or marked with cairns.

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