Research indicates that people will only use open space if it is in the sun; thus thousands of acres of open space in every city are unused because they are shielded from the sun by buildings - whether public buildings and of private houses. For example, many modern buildings in the Northern hemisphere have plazas and gardens on the north side. At lunchtime the plazas are empty and people eat their sandwiches in the street, on the south side where the sun is. The same is true for small private houses.
A survey of a residential block in Berkeley, California confirmed that 18 out of 20 people only used the sunny part of their gardens. People living on the north side of the street did not use their back gardens at all, and not one person interviewed indicated a preference for a shady garden. Other research indicates the importance of open space being 'defined' by some kind of enclosure, such as wings of buildings, trees, hedges, fences, arcades, etc. The popularity of European city squares confirms this; those that are particularly used are always partly enclosed, but they are also open to one another, so that each one leads into the next.