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Map scale and measuring distance

Knowing how far you have to go helps you decide whether to push on, rest or turn back. The map scale tells you how distance on paper relates to distance on the ground.

Understanding scale

Scale is written as a ratio, such as 1:25,000 or 1:50,000. It means one unit on the map equals that many of the same units on the ground.

• At 1:25,000, 4 cm on the map is 1 km on the ground. This scale shows lots of detail, such as field boundaries and small paths.
• At 1:50,000, 2 cm on the map is 1 km. It covers a wider area with less detail.

Most maps also have a scale bar in the margin. It is the easiest way to measure without doing sums.

Measuring a straight line

1. Lay the edge of a piece of paper, or your compass baseplate, between two points.
2. Mark both points on the edge.
3. Hold the edge against the scale bar and read off the distance.

Many compasses have rulers for common scales printed on the baseplate.

Measuring a winding route

Paths rarely run straight. Use a piece of string or a thin grass stem and lay it along the route, following each bend. Then straighten it against the scale bar. Without string, break the route into short straight sections, measure each one and add them up.

Using grid squares

If the grid squares are 1 km across, you can count squares for a quick estimate. Crossing a square diagonally is about 1.4 km.

Turning distance into time

Distance alone doesn't tell you how long a walk will take. Hills slow you down. A widely used rule of thumb for a fit walker with a light pack is:

• Allow about one hour for every 5 km on the flat.
• Add about 10 minutes for every 100 metres of climbing.

Count the contour lines you cross going uphill to work out the climb. Then adjust for your group: rough ground, snow, darkness, heavy packs, tiredness or children can easily double the time.

Plan with daylight in mind

Work out when the sun sets and give yourself a margin. If your estimate means finishing after dark, choose a shorter route or start earlier.

The app shows the straight-line distance to your next waypoint, but remember the walking route may be much longer once you follow paths around obstacles.

This article is in the Grid Survivor app, searchable with no signal. Get the app · £4.99