Plan a Route Leg by Leg From the Map

Good route plans are written leg by leg. For each leg between two recognisable points, a junction, a saddle or a lake outlet, you want three numbers: how far, in which direction and how steep. Written on a route card, they let you check progress, choose a bail-out and navigate if the trail disappears under snow or fog. This guide plans a three-leg loop on a 1:24,000 topographic sheet with a 40 ft contour interval, using coordinates read from the map.

The route

The loop starts at a trailhead at 39.6460, −105.5880, climbs to a saddle at 39.6532, −105.6010, traverses to a lake outlet at 39.6418, −105.6150 and descends to a trail junction at 39.6335, −105.6040. The coordinates came from the map’s latitude and longitude ticks, but they could equally come from a GPS waypoint or an online map. The aim is to know, before setting out, what each leg demands.

Step 1: distance

The GPS distance calculator gives the straight-line length of each leg on the WGS84 ellipsoid: 1,373 m (0.85 mi) for leg 1, 1,745 m (1.08 mi) for leg 2 and 1,319 m (0.82 mi) for leg 3, 4.44 km or 2.76 miles in all. On the map, at 1:24,000, those are 2.25, 2.86 and 2.16 inches, which you can confirm with a ruler. The trail will be longer than the straight line, especially where it switchbacks. For a winding mountain trail, add 20% to 30% to the straight-line figure for an estimate of the walking distance, or measure along the trail with a piece of string or a map measurer.

Step 2: bearing

The bearing calculator gives the initial true bearing for each leg: 305.7°, north-west, for leg 1; 223.4°, south-west, for leg 2; and 134.4°, south-east, for leg 3. Over legs this short, the great-circle bearing changes by less than a hundredth of a degree, so the initial bearing is the bearing for the whole leg. A hand compass reads magnetic bearings. In central Colorado the magnetic declination in 2026 is about 7.5° east, so subtract it: leg 1 becomes about 298° magnetic, leg 2 about 216° and leg 3 about 127°. Check the declination printed on your map against a current geomagnetic model, because older sheets show values that may be several degrees out of date.

Step 3: grade from the contours

Count the contour lines crossed on each leg. Leg 1 crosses 12 lines climbing to the saddle, a rise of 480 ft; over 2.25 inches at 1:24,000, a run of 4,500 ft, the map slope calculator gives an average grade of 10.7%, an angle of 6.1°. Leg 2 crosses 9 lines, 360 ft, over 2.86 inches: 6.3%, or 3.6°. Leg 3 descends 5 lines, 200 ft, over 2.16 inches: 4.6%, or 2.6°. Leg 1 is clearly the hard part. If its contour lines bunch together in the middle, measure that section separately: 6 lines over 0.6 inch would be 20%, an angle of 11.3° and a steep climb that the 10.7% average hides.

Step 4: the route card

A simple card for this loop would read: Leg 1, trailhead to saddle, 1.37 km, 298° magnetic, +480 ft, average 11% with a steep middle; Leg 2, saddle to lake outlet, 1.75 km, 216° magnetic, +360 ft, 6%; Leg 3, outlet to junction, 1.32 km, 127° magnetic, −200 ft, 5%. Add the features you expect to pass, such as a stream crossing or a cairn, and an escape route from the highest point. Many hikers add a time estimate from their own pace on similar terrain; your own records are better than any formula.

Common mistakes

• Planning with straight-line distance alone. It underestimates walking distance, sometimes by half on switchbacks.
• Forgetting declination. A 7.5° error over 1.7 km puts you about 230 m off line.
• Using the wrong contour interval. Some sheets switch to supplementary contours in flat areas; read the margin.
• Averaging away the crux. Measure the steepest part of a leg separately.
• Confusing percent grade with degrees. A 20% slope is 11.3°, not 20°.

Route card checklist

1. Break the route into legs between features you will recognise.
2. Read or record the coordinates of each leg end.
3. Find the distance of each leg and add an allowance for winding trails.
4. Find the true bearing and convert it to magnetic with the current declination.
5. Count contours and work out the average grade, then measure steep sections separately.
6. Write the card with escape routes and keep it with the map.