In diagnosing the city as an ecosystem, it is wise to work with black boxes. These are areas, factors or elements excluded from the main subject being considered or diagnosed. Black boxes strengthen the focus and avoid distraction. The black boxes are:

• An ecosystem is upwards and downwards interconnected with other levels. All different levels are excluded if considering a certain level. Most of the time in this book, we choose the city as our preferred level, but region, province or country (higher) and neighbourhood or district (lower) are also possible.
• The organisms of the ecosystem city are organisations. Their governors, managers and employees are considered included as the organs of an organisation, with the implicit acceptance of their personal performance and behaviour. An exception is made for governmental organisations with formal democratically elected and governing councils because they behave like organisations.
• All physical, geographical urban structures of streets, squares, buildings or houses within the city.
• External trends and developments of related data from outside are accepted as they are and will not be involved.
• The city’s general environment is accepted as it is and is not analysed, judged or validated as such and in the black box.