This map shows you by the different colours which London railway station you have to arrive to or leave from depending on your origin or destination, respectively.
EUSTON if you travel to or from the Western England, Scotland and North Wales. (Glasgow, Blackpool, Liverpool, Manchester)
MARYLEBONE if you travel from or to a small area of Northeast London.
PADDINGTON if you travel from or to South Wales, Somerset. (Cardiff, Bristol, Oxford, Reading)
WATERLOO if you travel from or to the South West: Devon & Cornwall. (Plymouth, Exeter, Southampton)
VICTORIA if you travel from or to the central South coast (Portsmouth, Brighton)
LONDON BRIDGE if you travel from or to the South West coast (Canterbury, Dover)
FENCHURCH STREET if you travel to or from East Anglia.
KINGS CROSS if you travel to the Eastern England & Scotland (Edinburgh, Leeds, Hull)
St PANCRAS if you travel from or to the Midlands & the Eurostar train to/from the continent (Paris & Brussels).