a window space projecting outward from the main walls of a building and forming a bay in a room, either square or polygonal in plan. The angles most commonly used on the inside corners of the bay are 90, 135 and 150 degrees. Bay windows are often associated with Victorian architecture. They first achieved widespread popularity in the 1870s. The windows are commonly used to provide the illusion of a larger room. They are used to increase the flow of natural light into a building as well as provide views of the outside that would be unavailable with an ordinary window. It is perhaps for these reasons that bay windows have become an architectural staple in San Francisco, a city of limited space.