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Maps, slope & daylight

Map scale, slope from contour lines, grade versus degrees, magnetic declination, sunrise bearings and how much daylight is left.

A map, a compass and the sun’s timetable answer most route questions before you leave. These guides turn millimetres into metres, contours into gradients, magnetic bearings into true ones and sun times into a plan.

  1. 01
    5 min read

    Calculating slope from contour lines on a paper map

    Calculate slope from contour lines: rise from the contour interval, run from the map scale, then grade and angle, with a worked 1:25,000 example.

  2. 02
    5 min read

    Percent grade and degrees describe the same slope in two ways

    Convert percent grade to degrees and back with the formulas, a conversion table, a worked 8% example and the error in the small-angle shortcut.

  3. 03
    5 min read

    How to read map scale, and what it does to distance readings

    Map scale explained: 1:25,000 means 1 mm is 25 m on the ground. Convert map distance, compare common scales and measure winding routes accurately.

  4. 04
    5 min read

    Magnetic declination: converting between true and magnetic bearings

    Magnetic declination: add east declination to a magnetic bearing to get true north. Conversion examples, bearing error per kilometre and a current value source.

  5. 05
    5 min read

    Sunset is not the end of usable light: planning a walk-out by the clock

    Work out how much daylight is left: NOAA sunset assumes 0.833° of refraction, and twilight ends 6°, 12° or 18° below the horizon. Worked example.

  6. 06
    5 min read

    Choosing a tarp or tent face for the morning sun, by season and latitude

    Find sunrise and sunset bearings by season and latitude, with a table from 0° to 60° N, and set a tarp’s open end for morning sun or shade.