Measuring on a map · 4 min
Distance and direction between two points
Why the shortest route looks curved on a map, and how to read a compass bearing.
Measuring on a map
A straight line on a round Earth
The shortest path between two places on a globe is called a great circle. It is what a plane follows, and what MapGO measures when it gives you a straight-line distance.
Flat maps have to stretch the round Earth to lay it out, so that shortest path usually shows up as a curve. The map is bent, not the route.
London to Los Angeles is about 8,756 km. The shortest route sets off north-west, up towards Greenland and northern Canada, although Los Angeles is far to the south of London.
Lesson notes
Everything from the cards above, on one page to come back to.
A straight line on a round Earth
The shortest path between two places on a globe is called a great circle. It is what a plane follows, and what MapGO measures when it gives you a straight-line distance.
Flat maps have to stretch the round Earth to lay it out, so that shortest path usually shows up as a curve. The map is bent, not the route.
London to Los Angeles is about 8,756 km. The shortest route sets off north-west, up towards Greenland and northern Canada, although Los Angeles is far to the south of London.
Direction as a number
A bearing is a direction written as an angle, counted clockwise from north. North is 0°, east is 90°, south is 180° and west is 270°.
Halfway between two of those is the in-between direction: 45° is north-east, 135° is south-east, and so on round the circle.
True north or compass north?
MapGO gives a true bearing, measured from the geographic North Pole. A magnetic compass points at magnetic north, which sits somewhere else and slowly moves.
If you will walk a bearing with a real compass, add or subtract your area's magnetic declination first. For maps and planning, the true bearing is what you want.
Questions
Is a bearing the same as an azimuth?
For everyday use, yes: both are an angle clockwise from north, from 0° to 360°.
Why does the bearing change along a route?
On a round Earth the shortest path keeps changing direction relative to north, except along the equator or due north and south. The bearing MapGO shows is the one you set off on.