People walk along a walkway between tree-like structures called 'supertrees' dominate the 'Gardens by the Bay' landscape with heights of up to 50 metres. These vertical gardens perform a multitude of functions such as providing shade and working as environmental engines for the gardens. They are fitted with environmental technologies that mimic the ecological function of trees. Photovoltaic cells that harness solar energy which can be used for some of the functions of the supertrees, such as lighting and collection of rainwater for use in irrigation and fountain displays. The supertrees also provide some air intake and exhaust functions of the conservatories' cooling systems. Gardens by the Bay is an integral part of a strategy by the Singapore government to transform Singapore from a 'Garden City' to a 'City in a Garden'. With a growing urban population, high-rise buildings are an increasingly prevalent feature cities across the world. Land is a major constraint in most Asian cities and in the face of high-density urbanisation, the only way to build is upwards. In the dense, urban environment of Singapore, where land area is severely limited, high-rise buildings have typified the urban fabric for years.