  the piccadilly line  is a line of the london underground, coloured dark blue on the tube map. it is the fourth busiest line on the underground network on the basis of the number of passengers transported per year with 210,000,000. it is mainly a deep-level line, running from the north to the west of london via zone 1, with a number of surface sections, mostly in its westernmost parts. of the 53 stations served, 25 are below ground. some of its stations are shared with the district line and some are shared with the metropolitan line. it is the second longest line on the system, after the central line, and has the second most stations, after the district line. it serves many of london's top tourist attractions including harrods, hyde park, buckingham palace, piccadilly circus (after which the line is named), leicester square and covent garden, as well as london heathrow airport, the busiest airport in europe (based on passenger numbers). ==history== ===the beginnings=== :see great northern, piccadilly and brompton railway for detailed histories of the great northern, piccadilly & brompton railway (gnp&br), the great northern & strand railway (gn&sr), and the brompton & piccadilly circus railway (b&pcr). the piccadilly line began as the great northern, piccadilly & brompton railway (gnp&br), one of several railways controlled by the underground electric railways company of london (uerl), whose chief director was charles tyson yerkes, although he died before any of his schemes came to fruition. the gnp&br was formed from the 
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