Scale of Maps and Charts – Ibex Aviation Academy

Scale of Chart

Scale is the relationship between distances on chart and on ground
The relation can be give as a Graduated Scale Line, Statement in Words and as a Representative Fraction
Graduated scale line is a visual representation of scale on a graduated line
Graduated scale lines are useful for visual estimation of distances
Statement in words is the scale explained as a statement
A statement of ‘One inch is equal to twenty nautical miles’ means a length of 1 inch on chart is equal to 20 NM on ground
Statement in words are useful when we want to use the normal inch scale to measure distances
Representative fraction is the ratio of chart length to earth distance without units
Statement in words can be converted to representative fraction by converting the numerator and denominator to the same units

A Representative Fraction of 1: 500,000 can be used in any unit like Inches as well as Centimetres
1 : 1 Million means 1 inch on chart is equal to 1 million inches on ground
1 : 1 Million also means 1 cm on chart is equal to 1 million cm on ground

More detailed charts are called large scale charts while less detailed charts are called small scale charts
Large scale charts cover lesser area and have large representative fractions
Larger representative fraction needs a smaller denominator
Therefore, Half million chart has larger scale than one million chart
Small scale charts cover more area and have a smaller representative fraction
Smaller representative fraction needs a bigger denominator
One million chart has a smaller scale than a half million chart