The Four Streams Model is a metaphorical device to allow faculty (and students) in the Vertical Studios to track the degree of emphasis accorded to four broad aspects of architectural design in the studios they offer (and take).
The Four Streams are:

1. Ordering Systems

Geometry, Number, Form, Flow, Space, Structure (physical and non-), Generativity, Composition…

2. Human Factors

Program/Use, Intention, Occasion, Cultural Diversity, Health, Human Potential; Culture, Social Equity, Social Life, Perception, Experience, Meaning…

3. Construction

Methods, Materials, Fabrication/Assembly, Mechanisms, Infrastructure, Building Services (M+E)…

4. Contexts

Political, Economic, Ecological; Climate, Landscape; Urban or Rural Development; Conditions of Architectural Practice…
During the process of describing their studios for lottery, and in their published course descriptions, faculty indicate the relative volume (degree of emphasis) each stream will have, within the following parameters:
(1 + 2 + 3 + 4) = 100%
10% < 1, or 2, or 3, or 4 < 50%
At the end of the semester, students are surveyed as to what relative volumes they experienced, and the instructors are given the results.
The educational purposes of the model are as follows (i) to help students pursue their own interests and talents and yet achieve balance over several semesters before moving on to Advanced Design, (ii) to allow teachers to teach to their individual strengths and interests, (iii) to offer a framework for advising individual students, during the semester and during Portfolio Review (end of third vertical studio), and (iv) to help coordinate Vertical Studio curriculum and teacher selection such that, averaged over all Vertical studios offered each semester, each stream receives roughly equal emphasis.
It is understood that in architectural practice, as in any comprehensive architectural design project at school, the Four Streams run concurrently—mingling, as it were, into one river.