Scale (map)
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An important property of a map is the scale. It can be indicated by a scale bar and/or a ratio 1:n. This enables the map user to measure a distance on the map and determine the distance on the ground. These days maps are usually produced under the metric system which makes it easy to perform this task. Maps are usually produced at standard scale factors of (say) 1:10,000 or 1:50,000 or 1:100,000 and all you need to do is take a measurement on the map (in mm) and multiply that figure by the scale factor to determine the distance on the ground.
Calculation: Measure 466 mm on a map which is scale 1 : 50,000 ...
466 x 50,000 = 23,300,000 mm
ie 23,300 metres
ie 23.3 kilometres
However, maps from some countries may use imperial units, especially older maps. These maps displayed scale ratios but often they were of the form 60 chains to 1 inch or 2 miles to 1 inch, etc.
In this case measure mm on the map and multiply by the scale factor below (where 1 yard = 36 inches, 1 chain = 22 yards) ...
40 chains = 1 inch >> 40 x 22 x 36 >> 1 : 31,680 (scale factor) 60 chains = 1 inch >> 60 x 22 x 36 >> 1 : 47,520 (scale factor) 1 mile = 1 inch >> 63,360 x 1 >> 1 : 63,360 (scale factor) 2 miles = 1 inch >> 63,360 x 2 >> 1 : 126,720 (scale factor) 4 miles = 1 inch >> 63,360 x 4 >> 1 : 253,440 (scale factor)
Calculation: Measure 132 mm on a map which is scale 60 chains to 1 inch ...
132 x 47,520 = 6272,640 mm
ie 6,272.6 metres
ie 6.27 kilometres
Maps are sometimes referred to as "large scale" or "small scale". In this context scale is obviously relative. It is safe to say that a "large scale" map displays objects such that they appear relatively large. For example, an island displayed on a 1:10,000 map will appear larger than if it were displayed on a 1:25,000 map. Thus, the former is "large scale". What can be confusing is that for a map of a given physical size, say 11 by 17 inches, a "large scale" map will have a smaller geographic extent than a "small scale" map centred on the same point. Maps with a ratio of 1:50 000 or larger (for example, 1:40 000 would be larger) are considered large scale. Maps with a ratio of 1:50 000 to 1:250 000 are considered intermediate scale. Any maps with a smaller scale (for example 1:300 000) are considered small scale. (indirect quote from http://geography.about.com/cs/maps/a/mapscale.htm article titled: Map scale By: Matt Rosenberg)
You can find a good real life explanation of this on the Michelin UK Maps and Guides website Real life explanation
