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To Measure a Trail
As hikers, we usually want to know how long our planned hike is going to be. Distance, along with major elevation gains, is the easiest way to guess at how long the hike will take. These distances are usually given in various guide books and sometimes on signs at the tail head. But to be useful the measurements must be reasonably accurate and up-to-date. Trail maintainers and guide book writers have even more uses for accurate measurements. They need to know about the distances to all the interesting points along the way. The Appalachian Trail has even further uses for the measurements. Each segment of the trail has a trail assessment that is updated every year or two. The assessment includes even more information about features along the trail or on the trail corridor. All this information is cataloged in a database that is keyed off the distances from known points such as road crossings. Such trail assessments are useful for almost all trails, but that is a subject for another time.
There are several possible ways of measuring the distances along a trail. Crude measurements can be done with a map measuring tool and a map of the trail. These are rarely good to better than 10% and frequently much worse if the map doesn't show all the switchbacks. Short distances can be done fairly accurately by counting your paces as you walk the trail, perhaps with the aid of a pedometer. Such measurements start to get inaccurate for more than a few hundred yards or if the terrain is rough and it is hard to maintain a uniform pace.
The most accurate measurements are done with a measuring wheel which is rolled along the trail and has a revolution counter, frequently calibrated in feet or meters. I have modified my wheel to have a clipboard mounted on the handle for ease in recording data. Make sure you know what the wheel is measuring by measuring a full revolution along hard pavement and measuring it with a ruler. Even with a wheel there is plenty of opportunity for errors. The wheeler must be careful that the wheel does not slip -- especially problematic if the ground is snow or ice covered. Heavy new fallen or damp leaves or tall grass also cause problems for the wheeler as they may jamb the mechanisms. Rocks, steps, and downed trees also cause problems. For trees you can usually measure right up to the tree by turning the wheel sideways near it. Then hold the wheel so that it does not rotate as you pick it up and over the tree. You will be off by about the diameter of the tree but that should not effect the length of the trail significantly, perhaps a few inches out of a mile. For steps and rocks you can sometimes wiggle the wheel through gaps or guide it carefully to keep it in contact with the ground as you gently lift it a bit over sharp angles. For a steep rock face you may need a helper to hold the wheel as you scramble up. You may even need to just guess at short distances, a few 10s of feet, and remember to add them to the wheel readings by artificially rotating the wheel at the end of the difficult section which you have carried the wheel over without it rotating. For even better measurements, wheel the trail in both directions and average the results. If there are severe discrepancies, you should remeasure the problem areas. Good measurements should be within about 50 feet per mile or 1%. For very rough terrain, this may easily increase to about 2%. Such measurements are adequate because hikers walking such trails will take their own routes around difficult sections and hence walk more or less than you measured.
What should you record? In a word, everything that is a permanent feature of the trail. However you should also be doing a mini trail assessment as you go. So record any downed trees, missing waterbars, missing or confusing blazes, wet spots, etc. Recording the data must be done accurately and in a fashion that it can be repeated by someone else to get the same answer you got. This means carefully picking and describing the points you record so that they can be determined within a foot or two. If the trail starts at or crosses a road, use the middle of the road as the measurement point, similarly the middle of a stream. You might want to record both ends of a long bridge or section of puncheon. In any case, record the length and height above the water of all bridges -- these may have legal implications for inspections. Benchmarks, easily recognized elevation changes such as peaks and saddles, large distinctive rocks, sharp bends in the trail, trail junctions, streams, woods roads, and rock walls are all good permanent features to record. Wet spots, dead trees or the place you saw a bluebird are not permanent features. Record good viewpoints, significant stands of timber such as a hemlock grove, open fields, patches of laurel or other easily identified vegetation. Record if the trail or sections of it is handicapped accessible. Always err in the direction of recording too much data. It may come in handy later. For instance if a relocation is done in the middle of a section, good intermediate points mean that only the new relocation has to be remeasured, not the whole trail.
When you have completed the measurements, share them with others by sending them to your local trail club who should have some way of making the information available through their publications. The data is best kept in a database program rather than a word processor file. It is much easier to find things (e.g. all the bridges) and to make updates when trails are relocated. I have an extensive collection of data for the New York-New Jersey Trail Conference, including the Dutchess/Putnam Appalachian Trail and most trails in the East of Hudson area. I will happily act as a collection point for the rest of the area covered by the New York Walk Book.
Supervisor, Putnam County Appalachian Trail
New York-New Jersey Trail Conference
January 28, 1995
Submitted to Trail Walker and AT Register.