Islington is a neighbourhood in Greater London, England, and forms the central district of the London Borough of Islington. Islington was the location of the cave in which Arthur Dent lived during Earth's prehistoric period. Two million years later, exactly the same spot was the location of Fenchurch's home, a degree of symmetry common to Arthur's life.
It is also the place where Arthur met Trillian, then called Tricia McMillan, at a party - with the phone number that was the same as the probability of being picked up by a spaceship while floating unprotected in open space.
Behind the scenes
Douglas Adams himself spent a great deal of time with friends in the borough, especially when bouncing a number of his earliest iterations of stories around. He dedicated his novel The Hitchhiker's Guide to the Galaxy to the Arlingtonians, for tea and sympathy.