View this artwork by appointment, at Tate Britain's Prints and Drawings Rooms
This is a tracing or schematic enlargement, presumably for the watercolour exhibited at the Royal Academy in 1794 (Whitworth Art Gallery, Manchester).1 Compare Tate D00154 (Turner Bequest XIV A), which is on similar paper. See also a possibly slightly earlier tracing, Tate D00150 (Turner Bequest XIII E). A study of the porch alone, evidently made on the 1793 tour, is in the Lloyd Bequest, British Museum, London (1958–7–12–391).2
The sheet has been folded in half vertically.