Map Scale and Grid References Explained

The map says the next junction is "a thumb's width away". That tells you nothing about fuel or daylight. You need a real distance, and you need a way to say exactly where you are.

Problem one: how far is it?

Start with the scale. The scale of a map is the ratio of a distance on the map to the corresponding distance on the ground.¹ Map scales may be expressed in words, as a ratio or as a fraction.¹ Many maps also print a bar scale.¹

Here's what a ratio means. A scale of 1:50,000 means one centimetre on the map stands for 500 metres of real ground.¹ If you prefer inches, the same idea works with any unit. Only the ratio matters.

Words can be easier to picture. If a map says an inch to two miles and two villages sit about two inches apart, they're about four miles apart on the ground.¹

Using the bar scale

The bar scale is a short ruler printed on the map. Some modern British maps have three bar scales, in kilometres, miles and nautical miles.¹ Pick the one in the units you think in.

1. Lay a strip of paper along your route and mark the start and end.
2. Slide the strip against the bar scale.
3. Read off the distance.

For a bendy road, measure it in short straight pieces and add them up. A straight line across the map will always come out shorter than the road you actually drive.

Remember that map distance is flat distance. A steep, winding track takes longer than the number suggests, so give yourself spare time and fuel.

Problem two: which scale do I need?

A large-scale map covers a small area in lots of detail. A small-scale map covers a big area with little detail.¹ For driving a backcountry route, a small-scale map helps plan the overall trip. A larger-scale one helps at junctions and tricky sections.

In the United States, one well-known series is the 1:24,000-scale topographic maps.² Check each map's own margin, because scales and styles vary between countries and makers.³

Problem three: giving or reading a position

A grid reference names a spot using the map's grid lines. The grid is a set of straight lines printed across the map. Different maps use different grid systems, so the margin tells you which one yours uses.

One system is the Military Grid Reference System. A reference looks like this: 4Q FJ 1234 6789.⁴ It has three parts, and the last part is made of numbers: an easting followed by a northing.⁴

In MGRS, and on map grids read the same way, you read west to east first (the easting), then south to north (the northing).⁴ Many people remember it as "Read Right Up".⁴ Check your map's own margin for how its grid is read.

The digits in the numerical part must come in an even number, split between easting and northing.⁴ More digits means a smaller square, so a more exact spot.

A quick way to practise

At home, pick a bridge or a junction on your map. Write its reference. Hand the map to someone else and see whether they find the same spot. If they don't, check you didn't swap easting and northing.

If you ever need rescue, a clear reference beats "somewhere past the creek". Learn to read one before you need it.

To work out where you are in the first place, see how to read a topographic map. A phone can also show coordinates, and what a GPX file is explains how they get stored.