Virtually every telephone exchange in Europe was named for its local area (village, town, or city). However, in the largest cities it was clear as early as the 1880s that several exchanges would be needed. These were usually given names reflecting a district of a city, for example "Holborn" in London, "Docks" in Manchester, "Leith" in Edinburgh, or in some cases an entirely unrelated name, e.g., "Acorn" or "Advance" in London, "Pyramid" in Manchester, and "Midland" in Birmingham. As automated systems were introduced starting in the late 1920s, the first three letters of these names were used in the numbering plans for those exchanges. The 3L-4N system was notably used in the capital cities Paris and London, both examples of the "big-city" problem. Large cities served by many manual exchanges could only be converted to automatic operation gradually, which required a logistics of operating both types simultaneously for several years.