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Backcountry Trail Inventory: A GPS Application to Wilderness

Presented at the National Trails Symposium, November 16, 1998.

By John Burde
Department of Forestry, Southern Illinois University, Carbondale, Illinois 62901

Map of Illinois

Any succesful management program is dependent upon having sufficient information to make proper decisions about the resource. Many trail inventories in the past identified the location and extent of trails using topographic maps and aerial photographs. Others were mapped using a measuring wheel and compass. Both techniques were very time consuming and contained significant error.

Recent advances in military satellite technology has led to methodologies that allow describing trails more accurately, more speedily, and at a lower cost. GPS technology can be an excellent tool in trail management. Such technology is being utilized to map trails on the Shawnee National Forest. The steps used to map Shawnee trails are described below.

Field Data Collection

Mapping GPS begins with hardware selection. GPS units vary by size and weight, by accuracy limits, and by price. The unit we used provided accuracy to 2 meters and cost approximately $3000 including software. This GPS unit collected data from military satellites, as opposed to a base station. This unit contained options to map areas, lines, and/or points. The user simply activates the unit and walks at a normal pace along the trail, stopping to note unique points such as rail junctions or highly scenic viewpoints.

In order to collect usable three-dimensional data (and also time), four satellites must be in view, i.e., must be above 15 degrees above the horizon. Geological formations and heavy leaf canopies can seriously affect signal capture. In such situations, mapping must be temporarily stopped until another satellite comes into view.

Data Analysis

Currently, military satellites have "selective ability" for security purposes, Half of the time an error factor is introduced; correction files may be obtained from a variety of sources. GPS software utilizes field data files and correction files to produce a corrected trail map, accurate to 2 meters.

Geographic Information Systems

The corrected files can be exported to a GIS system which allows the trail maps to be enhanced by the addition of wilderness boundary maps, water course overlays, ownership overlays, or whatever is needed by the trail manager. GIS can be used to compile trail distances and aggregate trail mileage. The GIS maps may then be used in desktop publishing software to create brochures, maps, and plans. GPS makes trail mapping cheaper and more accurate and is extremely easy to use. Trail mappers would be wise to consider GPS applications for their trail inventory needs.

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