The opening shot of Dickinson's Gaslight tentatively crosses the square, from the street sign on one side to the house at number 12 that will be the locus of the drama:
Pimlico Square is not a real place, though it is shown to us on a map:
In situating Pimlico Square, the film takes great trouble to redraw the map of Pimlico, placing the fictional square between real streets and squares:
On the map below, from 1939, Pimlico Square would be just above the 'GE' of Cambridge Street:
This post is adapted from a Cine-Tourist post for The Daily Map, here.