Until the 1930s, official maps of the fast growing metro networks in the big cities were mostly topographical and increasingly cluttered. Something had to be done to make them clearer. In 1933, the draughtsman Harry Beck came up with a schematic map for London Underground that resembled the diagram of an electronic circuit with its straight lines and 45° angles. The simple design had been so efficient and popular that in the following decades, nearly all urban transportation systems around the globe have adopted this style for their official maps.
The station density in the city centre is usually much higher than in the suburbs, so tagging every station with a name becomes a problem in the design of to-scale maps. Schematic maps get around this problem by blowing up the city centres and shortening the radial lines. This makes them more compact, while straightening the lines and omitting geographical details makes them much easier to read.
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The first diagrammatic map
London Underground had more or less cluttered geographic Tube maps until Henry C. Beck (also known as Harry Beck) developed the diagrammatic map in 1933 . Beck's thoroughly composed map design combines the clarity of straight lines with the use of basic colours. Berlin came up with a diagrammatic suburban rail map at about the same time.
In the Moscow map, the circular line and the angles of the other lines are contrasting nicely as the Koltsevaya line strikingly breaks with the 45° rule. All metro systems with ring lines should consider doing this in their maps (at least when the geography allows it, unlike the complicated, elongated circle in London). The only other known example is Nagoya's map with an ovoid depiction of its circle line.
For no apparent reason, Madrid came up with a rectangular map in 2011. It proves that using only 90° angles is rather confusing and does not really enhance usability. After many protests, it was soon replaced with a version similar to the formerly used 45° map styles.
New York is the world's only major metro system currently without a diagrammatic map. Official maps have been diagrammatic from 1958 but switched back to freestyle in 1979 . The current map is rich in geographic details yet not to scale. Critical voices are becoming louder recently and several suggestions have been made for diagrammatic maps.