In 1904, Paul Otlet (1868-1944) and Henri La Fontaine began to publish their classification system, the Universal Decimal Classification (UDC), developed from the Dewey Decimal System. The UDC is still used today in libraries outside the English-speaking world and at the BBC Archives. Otlet used drawing as a technique of ‘visual thinking’, often working with symbols and shapes of which the circle was his favourite. Tan’s drawing here presents Otlet’s circular diagram demonstrating the UDC system.