In the first phase, the built environment system is dismantled into its parts and the relationship between parts is being investigated. Accordingly, the performance of the system is being evaluated in the second phase and intervention plans are being formulated. In the third phase, design/modification scenarios are being tested with the same means that the actual context was investigated, and the last phase is dedicated to overall optimization through the definition of local retrofitting strategies.
Heretofore, IMM defined the main morphological subsystems (Horizontal Investigation), theorized the synergy between them and outlined the structural attributes emerging from their symbiosis (Vertical Investigation), and relied on a long list of indicators to evaluate the performance. The concentration of the current doctoral research would be on redefining the fusing mechanisms that shape the structural attributes of the system in phase one and the manners that these mechanisms are described to govern the performance of the system in the bridge between phases one and two.
The generic morphological subsystems recognized by IMM are namely: urban built-up, urban void, Types of Uses, and Links. The first two include all the physical elements such as buildings, parks, roads, canals, parking areas etc. and could be compared to a computer’s hardware. The latter two, however, is the utilitarian elements like means of transports, jobs, and services which could be interpreted as the software in the computer metaphor. It is necessary to note that the capacity of the system is resulted from fusing the physical and utilitarian elements together.
Although the city is a multi-final system with which a vast number of characteristics and purposes could be associated, there is relatively a small room for misunderstanding the morphological components as defined here. However, as it was argued in the previously, the key to understanding the city as a Complex Adaptive System is not its reduction to its parts but is having a deep inquiry into the relationships between parts. Now that the components are manifested, the question is how to study their fusing mechanism.
Scientifically, plentiful ways could be defined to study the relationships between the urban basic layers. Nonetheless, this study tends to hold to its purpose that is to deliver a clearer understanding of the systemic behavior of the built environment. Thus, every concept that is to be defined here has been thought only as a tool to illustrate certain dimensions in which morphological arrangements influence the operational behavior, and of course, does not necessarily defy other points of views from which the urban arrangement could be looked at.
With introducing IMM to the scientific community, Tadi and V. Mansesh identified the term "Vertical Investigation" that is the main procedure for explaining the behavioral manner of the city \citep{Manesh_2011} . In Vertical Investigation, each of the four basic components has been asynchronously linked with the others and gave birth to a number of conceptual attributes named Key Categories. Key Categories, hence, are bi-cellular entities of which each cell is one of the basic layers. By this definition, there is the possibility for six Key Categories to exist which have been identified by IMM as Porosity, Proximity, Diversity, Interface, Accessibility, and Effectiveness (formerly Efficiency).
The role of Key Categories is to decode the patterns of integration that the basic subsystems make with each other and define the working manner of the whole system. In IMM, they are the final explanation for the morphologically-propelled behavior of the spatial systems. That is to say, important operational traits such as spatial configurations, functional arrangements, travel behavior, and the quality of movement are being justified through them.
Assuming that the functioning manner of the system is portrayed by the Key Categories, IMM goes on and evaluate the performance of the system. But, before investigating the transmission from analysis to evaluation, It seems fundamental to review the architecture of the Key Categories.
If the Key Categories are to be restructured, then the most fundamental act seems to be defining an inclusive fusing process producing functioning attributes by addressing more than only two layers. It is worthy to mention that this new arrangement does not necessarily question the practical meanings of the Key Categories, but offers a new way of thinking to them in a systemic perspective.
Here, it is worthy to point that neither in the built environment nor in any other types of complex systems the true functioning mechanism of the system's components can be understood and described fully \citep{Hayenga_2008} \citep{Rouse_2015}. As the functioning characteristics of any system are defined chiefly by the interconnection of its subsystems \citep{Ramage_2009}, it seems that the unfillable gap in understanding the manners of complex systems operation is rooted the inability to comprehend their fusing rules. Substantially, there is a profound oneness between integrity and purpose in complex systems as though by functioning, the system is only unfolding its simultaneous multi-dimensional organic unity; the fusion happens at the very same moment of performing, and because at any stage the system completely adapts to the whole newly introduced circumstances, this process is perfectly unique at each given point in time. That is in fundamental contradiction with any human modeling logic which, no matter how profound, it is inevitably based on sequential procedures.
Thus, the practical attitude for approaching the complex system is to identify certain categories of outputs through which certain dimensions of the operational mechanism could be partially described. That is to say that the synthesis between parts can be only manifested in forms of conceptual structures which are necessarily inspired by a specific range of outputs related to a certain area of the system's performance. Obviously, the area of performance should reflect the problems that the ultimate model is going to address. Therefore, the improper situations must be identified and the problem should be influenced in a way that after forcing the intervention, those situations be mitigated (Poli 2013).
As the main interest in this research project is to study the various patterns that the spatial arrangements could influence the environmental performance of the built environment, the relevant outputs are those which affect mostly the environmental impacts.
Apart from variation in energy demands in different types of uses, the ordinary procedures through which a city consumes or leaks energy are the utilization of the existing buildings and infrastructure, mobility (flow of people, goods, and information), and construction of new buildings and infrastructure. Because the utilization of buildings is more of a collective matter rather than systemic within the scope of this research, the optimization of energy consumption in buildings is a matter of retrofitting issue.
Accordingly, Key Categories are defined here based on the morphological attributes that directly or indirectly influence certain patterns of energy consumption and ultimately are measured by indicators which address the figures of energy. Since there are a vast number of sustainable indicators verified by the literature on which this study can conveniently rely, the main challenge of this doctoral thesis is to define a solid structure for understanding the morphological attributes through the Key Categories (structural tools) and proof their relationship to the indicators as the evaluation tools.
Operational Facets
By nature, the true interactions between the components of the complex systems cannot be fully understood and modeled \citep{Harel_1987} . The main obstacle for that is the non-linear dynamics inherent in the functioning mechanisms of such systems (that is especially explicit in biological systems) while even the most advanced simulation algorithms are based on hierarchical arrangements that prevent them to be absolutely simultaneous. Therefore, modeling the way that the basic morphology generator elements of the built environment are fused with each other and form the Key Categories is more a matter of coherency rather than accuracy. Now, the question is in what the coherency of Key Categories lies?
By the definition, Key Categories are the conceptual apparatus with which the concealed morphological attributes of the urban contexts are being explained. These attributes are the structural affiliations that directly influence the patterns through which the system performs. Hence, as the structural tools, the most important factor for the Key Categories to be coherent is the presence of logical links that can inspire their relationship to the evaluation tools.
There could be various ways to conceptualize of urban elements fusing in an inclusive manner. One could be adding them up one after another and try to theorize meanings from the hierarchy of layers. For the number of layers is four, in this way the number of resulting Key Categories would be naturally 24. However, as it was explained before, complex systems do not function in hierarchical orders. So, it seems more appropriate to reduce the sequential relationships in conceptualization as much as it is possible. Accordingly, this research suggests for the synergy of built environment elements to be studied on a non-hierarchical foundation formed by two of the urban elements followed by a hierarchical dynamism of the other two. In this way, the number of possible Key Categories is cut in half and the non-hierarchical base could be the ground from which both the morphological attributes and performance indicators would rise. The mentioned foundations are referred as "Operational Facets" in the current research.
The Operational Facet resulting from Built-ups and Voids is the Spatial Configuration. The indicators related to spatial configurations are the ones involving the static distribution of spatial elements such as built-up density, the ratio of public voids, etc. If the dynamism added to spatial configuration begins with types of uses the resulting Key Category would be Porosity and if it begins with Links the Key Category would be Permeability which illustrates the quality of flow provided by given spatial configuration. With the same logic, other Operational Facets could be defined as Dynamic Density, Street network, Travel Points, Travel Distances, and Urban Currents (Fig2).