why is the representative fraction (rf) the universal standard for scale
Scale (map) Actual printed maps are produced from the projection map by a constant scaling denoted by a ratio such as 1:100M (for whole world maps) or 1:10000 (for such as town plans). To avoid confusion in the use of the word 'scale' this constant scale fraction is called the representative fraction (RF) of the printed map and it is to be identified with the ratio printed on the map. The actual printed map coordinates for the equirectangular cylindrical projection are
History of the metric system In 1837 the metric system was re-adopted by France, and also during the first half of the 19th century was adopted by the scientific community. In the middle of the century, James Clerk Maxwell put forward the concept of a coherent system where a small number of units of measure were defined as base units, and all other units of measure, called derived units, were defined in terms of the base units. Maxwell proposed three base units: length, mass and time. This concept worked well with mechanics, but attempts to describe electromagnetic forces in terms of these units encountered difficulties. By the end of the 19th century, four principal variants of the metric system were in use for the measurement of electromagnetic phenomena: three based on the centimetre–gram–second system of units (CGS system), and one on the metre-kilogram-second system of units (MKS system). This impasse was resolved by Giovanni Giorgi, who in 1901 proved that a coherent system that incorporated electromagnetic units had to have an electromagnetic unit as a fourth base unit.