In design, a typical approach is to simplify the problem, breaking complex reality/problems down into smaller parts that we can understand more easily and describe with models. This can be a necessary approach. However, what happens, if we miss important relations or variables? It can lead to sub-optimizations or even unintended negative impacts. Systems thinking aims to consider all relevant relations and variables. Hence, it has become more and more apparent that sustainability cannot be achieved through optimization of one object or element of a system, but that sustainability is rather a property of a system.
An introduction to this idea is provided by Eva Gladek in the following TED talk:
For sustainable planning or design, an integrated approach is required that considers systems-thinking including life cycle understanding and is a process that requires experts from different disciplines working together. Ann example of a framework for sustainable, integrated design and planning is “Symbiosis in Design” (SiD). Sustainable design and planning using SiD is based on the following definition of Sustainability that is being built on the three core components of equity, resiliency and autonomy: “Sustainability is a state of a complex, dynamic system. In this state a system can continue to flourish without leading to its internal collapse or requiring inputs from outside its defined system boundaries. Applied to our civilization, this state is consistent with an equitable and healthy society, as well as thriving ecosystems and a beautiful planet.” 
An introduction to SID. can be found here: http://wiki.ubc.ca/Documentation:Open_Case_Studies/CIVL/Resources.
An important tool within the SID framework is ELSIA, which is briefly described on the following website: http://wiki.ubc.ca/Documentation:Open_Case_Studies/CIVL/Resources.
The “Sustainable Urban Districts 2015 Global Review – Strategies to Accelerate Sustainable Urban Development”  presents 11 sustainable urban districts worldwide and presents the main lessons learned from evaluating those districts. A summary of the lessons learned (adopted from ):
Difference between traditional and sustainable urban development:
and includes material aspects such as CO2 emissions, energy use, renewable energy and material sourcing, conservation of ecosystems and species, contribution to local culture as well as catering to happy healthy living.
Exemplary approaches are “mixed use neighborhoods” and “building resiliency”.
Mixed use neighborhoods are to promote local employment, entrepreneurship, leisure, pleasant living and social involvement. This approach results in less need for transportation, promotes local economy, adds variety and overall creates an attractive and lively neighborhood. Mixed neighborhoods are more sustainable by promoting lifestyle change and being more resilient.
Building resiliency considers the traditional measure of a project in terms of market value being higher than the investment. However, beyond this measure it involves a more inclusive value proposition including social, cultural and natural values. A key aspect of building resiliency is to include (future) occupants in the planning. The project does not stop when buildings are delivered, but residence keep shaping the development of the community.
performance levels is particularly supported when investment decisions are based on total cost of ownership, as opposed to direct return on investment. These business models enable long-term involvement of developers and suppliers.” 
Strategies for sustainable development
Planning & optimization on a system’s scale that is too small leads to sub-optimization and unintended negative impact elsewhere