One of the most widespread conventions of urban design is the belief in the importance of ‘a sense of enclosure’. This term is defined by the City of Ottawa as
“when buildings physically define public spaces particularly through proportions between height and width in an area to create places that are comfortable to pedestrians.”
A sense of enclosure is routinely praised as a way to provide shelter from the elements, to provide a semi-private realm that feels like an outdoor living room, and to provide a sense of security due to the continuous or near-continuous building line creating ‘defensible space‘ and the overlooking buildings providing natural surveillance.
This article contends that the ‘sense of enclosure’ generated by following certain ratios of street height to street width is based on a valuable perception of what makes a satisfying place, but that the ratio theory is the wrong interpretation of that valuable perception. Consequently, by following the ratio theory we risk making developments that focus on concerns that may be unimportant to street users, and thereby make mistakes. In its place I’ll try to offer an interpretation of why some places that are said to ‘offer a sense of enclosure’ are satisfying that is both simpler and fits the data better, and which is constructed from two principles grounded firmly in known principles of how we perceive a place.