Boundary

From Tardis Wiki, the free Doctor Who reference
Boundary

In 1930, according to Michael Warner of the Central employment bureau of New York City, New Yorkers' had been leaving in their droves to search for work outside the city boundary. (TV: Daleks in Manhattan)

In the far future, the Boundary was a portal on the shore of an unnamed planet. (TV: Ascension of the Cybermen)