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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 Unit s, 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 ( " )
1 mile = 1 inch >> 63,360 x 1 >> 1 : 63,360 ( " )
2 miles = 1 inch >> 63,360 x 2 >> 1 : 126,720 ( " )
4 miles = 1 inch >> 63,360 x 4 >> 1 : 253,440 ( " )

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