Geography · Rung 12 of 12

Reading a real map

A topographic map states height with contour lines: each line joins points at the same elevation, and the spacing between them (the contour interval) is in the legend. Lines close together mean a steep slope; far apart, flat ground. Closed concentric rings are a summit if the heights rise inward, and a hollow if they fall. A V pointing uphill is a gully with water in it; a V pointing downhill is a spur. And there are three norths that do not coincide: true, magnetic (which drifts a few degrees a year) and the map's grid north; the difference between the first two is declination, and in Sweden it is a few degrees east.

Where this sits

Comes after
Mountains and plains, The map and its signs

Exercises from this rung

Generated by the app, from easiest to hardest

  1. On this map, where is the slope steepest?

    • Where they are furthest apart
    • Always in the middle
    • Where the line is longest
    • Where the contour lines are closest together

    Why Each contour joins points at the same height, and between one and the next there is always the same difference in elevation. If that difference is covered in little horizontal distance, the slope is steep: tight contours are a bank, and wide-spaced ones a plain. A cliff is contours so close they touch, which is why it is drawn with its own symbol.

    easier

  2. You see closed concentric contours. Summit or hollow?

    • It depends on the heights
    • You cannot tell without going there
    • Always a summit
    • Always a hollow

    Why The drawing is the same, so you have to read the elevation figures. Many maps help by marking hollows with small ticks pointing into the ring, called hachures. It is a neat case of a figure saying nothing on its own without its legend and its numbers: exactly what happens with a chart without axes.

    in between

  3. What is magnetic declination?

    • The angle between true north and the north the compass shows
    • The difference between north and south
    • The tilt of the Earth's axis
    • The map's projection error

    Why The north magnetic pole does not coincide with the geographic one and moves several kilometres a year, so the compass points off by an amount that depends on where you are and on the date. Topographic maps note it with its year and rate of change. On a short walk you can ignore it; on a long bearing, a few degrees of error become hundreds of metres.

    harder