LIKE a pair of sturdy boots, a good trail map is essential to a hiker and often taken for granted. Rarely are the painstakingly precise contour lines contemplated by the side of a mountain stream. But there are at least 200 people who won't look at the newest map of Mt. Washington and take it for granted.
Working during the past decade under the direction of master mapmaker Bradford Washburn, they volunteered time and energy to produce what most agree is the best map ever made of the New Hampshire giant - and 92.5 square miles of the Presidential Range.
Dr. Washburn and his wife, Barbara, have led geographic expeditions around the globe and mapped Mt. Everest, Mt. McKinley, and the Grand Canyon. But none of the Washburns' other mapping exploits compares to the one they have just finished.
``Mt. Washington is without a slightest doubt the most complicated thing I have mapped anywhere. Mt. Everest is a cinch compared to Mt. Washington,'' Dr. Washburn said in a recent interview at his Belmont, Mass., home.
``Measuring the trails was by far the hardest part of it,'' Mrs. Washburn said. The Mt. Washington map - unlike those of Everest and McKinley - shows some 200 miles of hiking trails. Thick forest in summer and snow in winter hide two-thirds of these trails from aerial view.
Mapping Mt. Washington was ``a people project,'' says Dr. Washburn. Volunteers who participated include people of all ages from places that range from New Hampshire and Virginia to India, Finland, and West Germany.
It took five seasons for the volunteers to plot the trails alone. Most were measured at least twice to make sure they were, as Dr. Washburn puts it, ``within a gnat's whisker'' of exact.
An effort that involved the Boston Museum of Science, the Mt. Washington Observatory, and the Appalachian Mountain Club (AMC), the new map contains 10 major White Mountain peaks and covers 8.17 miles east to west and 11.32 miles north to south.
The project began in February 1978. Alan Smith, who was then president of the Mt. Washington Observatory, asked Washburn if he could produce a relief model of the mountain for the observatory's museum in the new Sherman Adams Building on Mt. Washington's summit. He had in mind something similar to the three-dimensional Grand Canyon exhibit Washburn had produced for the Museum of Science.
``He agreed but said you've got to have a good map and there wasn't one that was good enough. And that's how the whole project got started,'' said Mr. Smith, of Concord, Mass., who volunteered throughout the endeavor.
The first step was selecting locations for control points - places easily identified on aerial photographs and of known longitude, latitude, and altitude. Dr. Washburn decided not to use the existing United States Geological Survey map as a base, but he did accept as true the USGS elevation of Mt. Washington at 6,288.176 feet.
Once the major control points were chosen, Washburn began the next phase of the project. The area had to be photographed twice from the air in overlapping north to south strips to provide the stereo quality needed for cartography.
The photos taken in early May showed parts of the mountains later hidden by leaves. Those taken in August provided a view of contours covered with snow in May. Both sets of photos were essential for a mapmaking step that would come much later - contour drawing by Swissair Photo and Surveys Ltd. of Zurich.
Before being photographed, the known control points had to be marked. To accomplish this, the Community Boat Club of Boston donated boat sails, and the AMC stockpiled them at its mountain huts until they were needed.
One day in August, volunteers took the sails to the control points ordered by Washburn, tied the tip of each sail to markers set into holes previously drilled into the rock, and unfurled the sails so that, from above, they appeared as white arrows pointing directly to the control targets.
Then volunteers began years of measuring distances and angles to produce a control network of triangles connecting all the basic control points.
One process employed to create the control network is called trilateration - measuring all three sides of a base triangle precisely. It works this way: The Washburns would set up an electronic distance-measuring machine (EDM) called a Ranger IV at a known location. Another volunteer - often Casey Hodgdon of Gorham, N.H. - would drive to the top of Mt. Washington and hike down to another survey station. Mr. Hodgdon and the Washburns would report their positions to each other using two-way radios.
Conspicuous targets painted hunter orange marked each survey station. Exactly above a drill hole, Hodgdon would hold a cluster of special prisms, at which Dr. Washburn would shoot the EDM laser.
The red light beam from the helium neon laser would bounce off the prisms and return to the Ranger IV, which calculated precise information on the distance between the two points. The Ranger IV's computer would then produce a digital readout of the distance. Mrs. Washburn took notes on the measurements, filling seven one-inch-thick notebooks.
All measurements were taken several times to ensure accuracy. Laser distances also needed to be adjusted for air pressure and temperature.
Dr. Washburn explained that when pressure is high or temperature is low, the air is thicker and slows the light beam. From summer to winter, a 10-mile length measured by laser can vary 6 or 7 feet.
The mapping process became more complicated below treeline and consumed a major portion of the project's work and time. Here Hodgdon's intimate knowledge of the White Mountains was invaluable.
Hodgdon spent six years as a weather observer at the Mt. Washington Observatory and 11 years as range patroller with the US Forest Service.
``Basically, I've lived my whole life up here in the mountains,'' said Hodgdon, who now works for the Gorham Department of Public Works. ``So I was familiar with the trails.''
When they were mapping below treeline, the Washburns would set themselves up at a known point, and Hodgdon or other volunteers would hike down a trail, looking for a break in the cover, a peephole through which they could see the couple and position the prisms.
``We had a lot of challenging days,'' Hodgdon said. ``Everything hinged on being physically able to see clearly between Point A and Point B.''
Washburn said that ``a good deal'' of the work was done at night. The air is smoother at night, he explained, and prisms are more readily visible. When days were warm, the team would often encounter boiling, a shimmering in the atmosphere caused by currents of hot air generated over rocks. This phenomenon prevented accurate measurements.
On each hidden trail, the mapmakers determined about 10 known points. Teams of volunteers walked the trails with a compass and 100-foot tape to fill in the distances in between. On the map, three inches represents one mile - and a lot of walking.
After the trilateration and trail measuring were finished, the mapping project shifted gears. Dr. Washburn now fitted his control network of lines among and between control points into the New Hampshire survey grid - a system of coordinates for the state. Then the work moved to Switzerland, where field data were plotted and contours drawn.
``You can't get a really gorgeous map like that made in the US,'' Dr. Washburn said, referring to the delicate contours and cliff shading that really look like mountains. ``The Swiss are very committed and fascinated by detail. Some people would say this is unnecessary perfection. But if you make a map topographically almost perfect in its detail, all of a sudden the whole map looks like reality.''
Swissair Photo and Surveys Ltd. used a piece of equipment called a Wild A-8 Plotter to match the stereo aerial photographs with the control network, and to achieve the proper scale. Orell Fussli & Co. of Zurich printed the map in light green for vegetation, blue for water, and gray for bare rocks.
It cost about $280,000 to produce the new Presidential Range map - that doesn't include what it would have cost to pay the volunteers. The project was financed largely through donations.
Five thousand copies of the finished 29-by-40-inch map arrived in Boston in May. They are for sale by the AMC.
For information about the map, write to Appalachian Mountain Club, 5 Joy St., Boston MA 02108.