Architectural plans are design diagrams that describe building layout where space is planned according to design requirements. Style in architecture is generally characterized as common features appearing in a particular class of building design. This research seeks to address how to recognize architectural design style from a 2D plan diagram. We explore this question in a computational encoder-analyzer (E-A) model for 2D plans, where a characterization of 2D style is based on qualitative spatial representation and information theo- retic measures. In a preliminary study of a prominent architect’s plans, we demonstrate the effectiveness of our approach. We conclude by discussing practical applications of automated plan recognition and classifi- cation in design support tools. Introduction Research in various domains share problems of formaliz- ing style. The architectural design domain is no exception, and in most cases, “style” is difficult to determine formally. In all visual domains, style is commonly used to describe consisten- cies among artifacts that are the product of an individual, culture, period, or region. In this way, the concept of style in architecture acts as an ordering principle, allowing building designs to be structured or categorized, providing order within an otherwise apparently chaotic domain (Knight, 1994). The style of a building can be based on a number of dif- ferent representations and evaluated using a variety of at- tributes. Here, two principal aspects concern us: (a) the visual representation, which can be two (2D) or three dimensional (3D); and (b) the physicality, which can encompass a vari- ety of perceptual primitives. For the former aspect, we have chosen to focus our attention on 2D representations and utilize plan diagrams as our analytical vehicle. While acknowledging alternative approaches to architectural style, we limit our scope to 2D plan diagrams and consider this mode of design representation and communication as a significant artifact upon which to consider the problem of characterizing architectural style. For the latter, our approach to physicality distinguishes two criteria: (a) shape elements and (b) their spatial relationships, which Shapiro (1961) considered significant for the characterization of style. Thus, both open and closed shapes as well as relations describing contact and organization can be recognized visu- ally from 2D contours. Using this approach to representation as our foundation, we present an encoding-analysis model capable of identify- ing and comparing 2D plan diagrams. Our objective is to derive both local and global features as stylistic discrimina- tors. We define stylistic discriminators as those features which remain approximately invariant within a design, but which vary between individuals, cultures, periods, or regions. Specifically, we explore how to formally recognize building plans, detect features salient to assessing style, apply mea- sures of both similarity and complexity, and ultimately iden- tify the design style. We show that 2D plan diagrams contain both local and global features that are significant in discrim- inating between and categorizing designs. The remainder of this article is divided into six sections. A survey of related work is carried out in Section 2. Qualitative representation of 2D plans and the information theoretic tools used in measurement are described in Section 3. The approach is demonstrated in a study on Frank Lloyd Wright’s residential building plans over five decades, and the results are presented in Section 4. Section 5 discusses various issues of this approach, and Section 6 concludes the article. Background A 2D plan diagram is a primary mode of building design representation and plays a central role in design communica- tion. Before buildings are constructed, the problem of space allocation has typically been explored and solved in a number of conceptual sketches. The final sketch is then formalized in a set of technical plans to facilitate construction. JOURNALOF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, 57(11):1537–1550, 2006 A Qualitative Feature-Based Characterization of 2D Architectural Style Julie R. Jupp and John S. Gero Key Centre of Design Computing and Cognition, G04, University of Sydney, Sydney, NSW 2006, Australia. E-mail: {jupp_j, john}@arch.usyd.edu.au Accepted March 24, 2005 © 2006 Wiley Periodicals, Inc. • Published online 14 July 2006 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/asi.20430