In nature, the principle of ecological efficiency is linked to the amount of energy that complex systems, organisms and ecosystems can produce over time. For example, the most complex system we know, the human species, has the energy capacity equivalent to a 150 watt light bulb. When a person eats, that food can be converted into energy and physical activity. The more food a person consumes, the higher their ecological efficiency because they need to exude more effort to convert their food into energy and physical activity. In relation to a system, the energy required to maintain and conserve a system is higher if there is a larger amount of damaging resource consumption. Therefore, the ecological efficiency of non-sustainable practices in nature is high (ecologically inefficient), as nature cannot produce enough energy to maintain its natural organization when it is being exploited. "Maximizing entropy in terms of information" is an expression from academic ecology that describes the principle of ecological efficiency discussed above.

In urban systems, this ecological efficiency can be calculated using the guidance of the sustainability equation. In an urban system working towards sustainability, the sustainability equation should yield shrinking results.

For urban systems, we can express efficiency using the following equation:


This function should result in declining values as sustainability increases.

This ratio can also be turned into a synthetic equation:

This equation is the guiding function of urban sustainability, where E represents the consumption of energy (as a synthesis of resource consumption); n is the number of legal persons in an urban environment (economic activities, institutions, facilities and associations); and H is the value of diversity among all legal persons, also called urban complexity (organized information).

In current urban systems, there is the tendency to promote production, and the sustainability equation is increasing where it should be decreasing (process towards urban non-sustainability).

The rate of energy consumption is significantly greater than the rate of organization. This is because economic logic bases its strategy on the consumption of resources to earn money. In fact, a region that is well-organized to consume a lot of resources actually has a competitive advantage economically speaking.

In Urban Ecology, promoted by BCNecologia and applied to the model of city development, the consumption function is minimized (and is in the process toward urban sustainability). This makes the maintenance and organization of resources rise in complexity, and the negative environmental impacts on the city decline. Therefore, an increase in the efficiency of the urban system is necessary for the development of sustainable cities.


<<The Sustainability Function is an equation that calculates where an urban system sits on a scale between sustainability and unsustainability. It is expressed by the equation (E/nH) where E is the consumption of energy; n is the number of legal persons in an urban environment; and H is the value of diversity among those legal persons, also called urban complexity.>>