Urban design works over a long time period. A fundamental difference between urban design and architecture is the passage of time. A masterplan creates a vision for an area that has to be translated into instructions (often called a design code or regulatory plan) for future developers and their architects. The scheme is implemented over many years, often without the involvement of the original urban designer. The key to success is therefore the clarity of the instructions, the balance of fix and flexibility and the way in which they are enforced