Garden design theory explains, or should explain, the 'What, Where, Why and How' of making gardens.

Many of the world's best-designed cities have been inspired by garden concepts.

Landscape planners will have the opportunity to make sculptured roofscapes, so that cities appear to be verdant hills and valleys. Streets will become shady routes carved through the undergrowth. Roofs will become mountain tops. People will become ants.

From 50 centuries, we can learn about the close relationship between garden design and urban design, because both arts involve the composition of buildings with paving, landform, water, vegetation and climate.

Modernism', as a label, has currency in the arts, architecture, planning, landscape, politics, theology, cultural history and elsewhere.

Having lasted for 4,000 years, the use of nature's materials to express ideas about nature may be expected to continue. The best garden designs are produced with an awareness of the art, science, history, geography, philosophy, social habits and construction techniques of their period.

There is much to learn about what could happen in the gardens of the future, should designers wish to learn about the past.