How to spot history in your OS map
Mary-Ann Ochota, OS GetOutside Champion & author of Hidden Histories: A Spotter’s Guide to the British Landscape reveals some of the most common archaeological clues you’ll spot on an OS map.
Have you ever got confused about what a map scale is, or wondered what is the difference between our Landranger and Explorer maps? Our quick guide to understanding map scales will help!
Choosing the right map scale can be really important when you are planning you adventures. Use a map with too little detail and it can be hard to use, while too detailed a map may mean you are continually going off the page or map sheet.
The critical item that tells you how much detail is shown is called the 'scale'.
The scale of a map shows how much you would have to enlarge your map to get the actual size of the piece of land you are looking at. For example, your map has a scale of 1:25 000, which means that every 1cm on the map represents 25 000 of those same units of measurement on the ground (for example, 25 000cm = 250 metres). That might sound a bit complicated, but OS maps have been designed to make understanding scale easy. Look at the front of a 1:25 000 scale map and you will see that the scale has been also written out for you like this:
4cm to 1km
This means that every 4cm on a map = 1km in real life. To make it even easier, the grid lines are exactly 4cm apart, so every square is 1km by 1km.
Maps are made at different scales for different purposes. The 1:25 000 scale map is very useful for walking, but if you use it in a car you will quickly drive off the edge! On the other hand, maps at 1:250 000 scale (note the extra zero) show lots more area, but in far less detail.
A map scale is the size ratio of a feature on the map to the one in the real world
Road maps: 1: 250 000 scale, shows roads and towns, but few individual features over a large area
Landranger maps: 1 : 50 000 scale, shows roads, large paths and some individual features
Explorer Map: 1 : 25 000 scale, shows many features including paths and buildings over a small area
Mastermap: 1: 1 250 scale, shows accurate position for individual buildings or small areas
The terms 'large scale' and 'small scale' are used to describe different scales. However, they can be confusing :
Large scale maps have low number is the scale, such as 1: 1250. The features are shown are large
Small scale maps have a high number in the scale, such as 1: 250 000. Individual features shown are small
High number = small scale
There is no fixed definition of what scale ratios fall into large scale or small scale.
More reading: Advanced guide to map scales
This is part of National Map Reading Week, which encourages everyone to improve their map reading skills and discover new adventures.