Flagging trail is the active step of following the concept lines (using GIS software) to place survey flagging on the ground for trail builders to follow during construction.
Completely scouting each concept line is not feasible so flagging is the final opportunity for planners to consider on-the-ground conditions. The presence of large trees, boulders or other factors are not possible to consider remotely when determining trail alignments.
Flag Lines & Field Grade Checking
Flags are strips of hi-visibility survey tape—hung on branches or twigs at approximately eye level—that mark the centerline of the proposed trail. Flaggers use analog or digital clinometers to verify that the grade between flags and the average grade of the line follows the spirit of the trail index.
This is a critical step to ensure grades are appropriate to match the desired experience and difficulty level of the trail. Builders generally construct trails within 15-25' of the flag line following the predetermined grade.