Measure Great-Circle Distance and Bearing on a Map

The Distance tool in TrueSize measures the shortest path along the Earth's surface between two points, called the great-circle distance, and also shows the straight-line distance through the Earth. The Bearing tool gives the compass direction from one place to the other. Both draw the line on the map, and on a flat map that line usually curves.

A distance measurement between two cities.

How to measure distance

1. Open the Tools tab of the ribbon.
2. Click Distance. The Distance tool opens, and a hint tells you to click two locations on the map.
3. Click the first point, then the second. The panel shows Point A, Point B, the Distance (surface) and the Distance (straight through Earth).
4. Add more pairs by clicking again. Click Clear all to remove them, or Exit distance tool when you are done.

You can also use the buttons in the header:

• Switch units toggles between kilometers and miles.
• Show distance rings and Hide distance rings draw concentric circles around the first point.
• Enter coordinates manually lets you type Point A Latitude and Longitude and the same for point B, then click Calculate.

Surface distance and straight-line distance

The two numbers mean different things.

Measurement	What it is
Surface (great-circle) distance	The shortest path along the Earth's surface. Planes and ships follow routes close to this.
Chord distance	The straight line through the Earth between the two points. It is always a bit shorter.

For two cities a few hundred kilometers apart the two are almost identical. For points on opposite sides of the world the chord is much shorter, because it cuts through the planet.

Why the line curves on a flat map

A flat map stretches the globe, especially away from the equator. The shortest path between two points on a sphere is an arc of a great circle, and when that arc is drawn on a Mercator-style map it bends toward the pole. This is why flights from Europe to North America cross Greenland or the far North Atlantic instead of following the straight line you would draw on paper. Switch to the globe (Style → Globe) and the same line looks straight.

Measure the bearing

The bearing is the compass direction (azimuth) you would face at point A to head toward point B along the great circle.

1. Open Tools and click Bearing. The Bearing tool opens with a hint to click two locations.
2. Click point A and then point B.
3. The panel shows Bearing / azimuth in degrees with a compass direction such as NE, along with the surface distance.

A bearing measurement with the azimuth in degrees.

Along a great circle the bearing changes as you travel, so the number is the starting direction at point A.

Tips

• Combine the tools with true-size regions: place a country on the map and measure across it to see how far it really spans.
• Use Show distance rings to see everything within a given distance of a point.
• For people counts inside a circle, use the population radius tool.

Examples to try

• Measure London to Tokyo and compare the line on the flat map with the globe.
• Measure the width of Greenland and then drag Greenland over Africa (see Greenland vs Africa).
• Find the bearing from your home to a place far away.

Where it works

Distance and bearing work on the web and in the TrueSize mobile app.

Related

• Population radius tool
• Move and compare regions
• Draw and edit shapes
• Customize the map appearance

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Next: Population radius tool