Geography · Rung 2 of 12

The map and its signs

A map is read with three things. Scale: 1:50,000 means one centimetre of paper is 500 metres of ground, and the smaller the bottom number, the larger the scale and the more detail. Coordinates: latitude runs from 0° at the equator to 90° at the poles and is measured in parallels; longitude runs from 0° at Greenwich to 180° in meridians, which converge at the poles, so one degree of longitude is 111 km at the equator and nothing at the pole. And projection: cylindrical (Mercator) for navigation, conic for countries stretched in latitude, azimuthal for the poles. None preserves angles and areas at once; Gauss proved that and there is no way around it.

Where this sits

Comes after
The map from here
Opens up
Mountains and plains, Rivers and lakes, Reading a real map

Exercises from this rung

Generated by the app, from easiest to hardest

  1. The point is marked on the grid. What are its coordinates?

    • 40° north and 20° east
    • 20° north and 40° east
    • 40° north and 20° west
    • 40° south and 20° east

    Why Above the equator is north and to the right of the Greenwich meridian is east. The usual order is latitude first, longitude second, which is the reverse of screen coordinates (x, y) and an endless source of bugs in programming.

    easier

  2. Which one always measures the same, a degree of latitude or one of longitude?

    • Latitude: 111 km anywhere
    • Neither: it depends on the projection
    • Longitude: 111 km anywhere
    • Both are always the same

    Why Parallels shrink towards the poles, so a degree of longitude is 111 km at the equator, about 57 in Stockholm and zero at the pole. Meridians, by contrast, are all equal great circles: a degree of latitude is always 111 km. That is where the nautical mile comes from, one minute of arc of latitude: 1,852 m.

    in between

  3. An equal-area projection (like Mollweide) preserves areas. What does it ruin?

    • Shapes: countries come out squashed or stretched
    • Nothing, which is why it is preferred
    • The areas near the poles
    • The order of the continents

    Why Preserving area forces angles to distort, so outlines stop looking like the real thing, especially at the edges of the map. It is for comparing sizes at a glance (population, cropland, epidemic cases) and useless for navigation. The general rule: pick the projection by what will be measured on that map, not by which looks nicer.

    harder