Why the compass disagrees with the map
A COMPASS needle does not point exactly to the North Pole at the top of a map. It points to the magnetic north pole, which is in a different place and slowly wanders; it has been drifting from Canada towards Siberia. The difference between the two, in degrees, is called magnetic declination, and it changes from place to place and year to year. Good walking maps print the current difference in their margin, so walkers can adjust a BEARING taken from the compass before following it on the map.
For a few years around the 2010s and 2020s, a strange thing happened in Britain: in some places the compass pointed almost exactly to the top of the Ordnance Survey map, for the first time in hundreds of years, as the line where the difference is zero crept slowly across the country.
Maps that became puzzles
The very first jigsaws were maps cut up to teach children geography, as our jigsaw puzzles page explains, and learning where places are is still the start of map skills. Knowing where you are on a map, and which way you are facing, is the next step.
Britain's national mapping agency, the Ordnance Survey, began after the Jacobite uprising of 1745, when the army realised it had no good maps of the Scottish Highlands. Its detailed maps use a GRID of numbered squares, so any place can be given a COORDINATE. The trick for reading one is to go along the corridor and then up the stairs: read the numbers across the bottom first, then the numbers up the side.
Reading the landscape
A map's LEGEND, or KEY, explains every SYMBOL. Many are clever little pictures: on British maps, a church with a tower is shown as a square with a cross, and one with a spire as a circle with a cross. The SCALE shows how much the real world has been shrunk: on a common walking map at 1 to 25,000, four centimetres on paper is one kilometre on the ground. CONTOUR lines join places at the same height, so lines packed close together mean a steep slope, and lines far apart mean gentle ground. A few maps also use shading, as if a light were shining from the top left, to make hills stand out.
Lines round the globe
Lines of LATITUDE measure how far NORTH or SOUTH of the EQUATOR a place is, and sailors could work them out from the height of the Sun or the stars. LONGITUDE, how far EAST or WEST, was much harder, as our inventions page explains. In 1884 delegates from twenty-five countries met in Washington and agreed that zero degrees of longitude, the Prime Meridian, would run through the Royal Observatory in Greenwich, London, where visitors can now stand with one foot in each hemisphere.
No flat map can show the round Earth without stretching something, just as you cannot flatten orange peel without tearing it; a GLOBE is the only true picture, and an ATLAS the handy book version. Each BORDER, ROUTE and DIRECTION on a map, and every point you PLOT, depends on the choices the mapmaker made.