In today's increasingly regulated cities, a noticeable pattern of open space between buildings and streets has emerged. The study shows that marginal spaces, defined as open spaces between buildings and the street, are generated as inevitable by-products of urban spatial development. Changes in both societal values and the regulatory processes of urban spatial development can transform marginal spaces into undesirable areas. In this paper, I argue that incidental generation and transformation of marginal spaces is inappropriate. Marginal spaces occupy a substantial proportion of urban land and deserve serious consideration.