The oldest part of what is now the District line opened on 24 December 1868, from South Kensington to Westminster. This map was hand-drawn as an exact record of the railway and where it ran. It was standard practice well into the 20th century to use existing, commercially produced street maps of London and simply print the railway line on top, usually in red. Maps of this period were large and functioned as street maps as well as railway maps, but as they got smaller they had to be simplified.