Maps & Scale

A ratio connects two distances

A scale of 1:25,000 means that one unit on the map represents 25,000 of the same units on the ground. The units must match before you convert them. One centimetre therefore represents 25,000 centimetres, which is 250 metres. The ratio describes a relationship, not a particular paper size.

A scale bar marks a ground distance directly on the map. If the entire image is proportionally enlarged, the bar enlarges with it. A printed numerical ratio no longer describes the enlarged image accurately unless it is updated.

Work through a route calculation

On a fictional printed map at 1:25,000, a straight line between two points measures 3.2 centimetres. Multiply 3.2 by 250 metres to obtain 800 metres. If a drawn path between the same points measures 4.8 centimetres, its modelled length is 1,200 metres. The route is longer than the straight-line separation.

This calculation does not give a travel time or establish that the path is usable. Slopes, crossings, surfaces and current conditions are outside the distance conversion. State whether you measured a straight line or followed the route.

Choose a view for the question

A larger-scale map, such as 1:10,000, generally covers a smaller area at a given printed size than a smaller-scale map such as 1:1,000,000. The apparently reversed wording comes from the fractions: 1/10,000 is larger than 1/1,000,000.

A topographic map represents land shape and other features using a key and conventions. A transport diagram may stretch distances to make connections easier to read. Neither is automatically wrong: ask what the map is designed to communicate before measuring it.

A map has a date and a viewpoint

Check title, source, date, legend and scale together. An old map may show a proposed road rather than one built at that time; a current-looking reproduction may contain historical information. All maps select details. An unmarked feature is not proof that nobody used or valued that place.