Using measures of cost distance in the estimation of polity boundaries in the Postclassic Yautepec valley, Mexico Timothy S. Hare* Institute for Regional Analysis and Public Policy, Morehead State University, 100 Lloyd Cassity Building, Morehead, KY 40351-1689, USA Received 8 December 2002; received in revised form 20 October 2003; accepted 27 October 2003 Abstract The reconstruction of polity boundaries is essential for the study of political evolution, but few enhancements to archaeological boundary estimation methods have been proposed in recent years. New techniques of terrain modeling and geographical analysis provide the means to augment traditional methods of boundary estimation. In this paper, I review archaeological methods for estimating the spatial location of boundaries between independent polities and ways to modify these methods to explore the processes of political expansion in the evolution of complex societies. I demonstrate several of these methods using data from Postclassic polities in the Yautepec valley, Morelos, Mexico. Through time, seven independent polities were founded, expanded, and were ultimately incorporated within two levels of regional political administration. I apply new quantitative methods for the estimation of polity territories and explore the processes that resulted in the formation of a regional polity. The resulting boundaries are objective estimates of the location of borders based on energetic efficiency that can be systematically tested against theoretical models. These estimated boundaries provide a basis for exploring the social meaning of territorial divisions. Additionally, energetic boundaries provide a means for delineating local zones for landscape utilization and comparative analyses.  2003 Elsevier Ltd. All rights reserved. Keywords: Aztec; Postclassic; Political expansion; Early states; GIS; Boundary modeling; Cost distance 1. Introduction Boundaries are fundamental components of most societies, but are difficult to study archaeologically. Regional settlement and artifactual distributions are the basis for many reconstructions of the spatial arrange- ment of past societies, providing data such as demo- graphic histories, settlement hierarchies, and societal classifications. Studies based on these data, however, demonstrate the difficulty in determining the locations of boundaries. For instance, unambiguous material markers of boundaries are difficult to identify, the distribution of particular artifacts often encompass mul- tiple polities, and changes in artifact frequency are often characterized by gradual change rather than clear dis- junctions. None the less, regional analyses often require the estimation of boundary locations between settle- ments, polities, and other analytical units to reconstruct the nature of individual polities and their interactions. In addition, the study of expansionary polities requires the estimation of how boundary locations changed through time. In this paper, I review archaeological methods for investigating the location of boundaries and simulating boundary changes using settlement data. I demonstrate some of these methods using diachronic survey data from the Yautepec valley, Morelos, Mexico. While each of the numerous types of social, econ- omic, and political boundaries deserve attention, in the present work, I focus on archaeological approaches to political boundaries and their locations. Kent G. Lightfoot and Antoinette Martinez’s review of archaeo- logical studies of boundaries and frontiers demonstrates that numerous social, political, and economic processes affect political boundaries [52]. Border studies require balanced perspectives that do not see peripheral people as inactive subjects, but that recognize such * Corresponding author. Tel.: +1-606-783-9436; fax: +1-606-783-5092 E-mail address: t.hare@morehead-st.edu (T.S. Hare). Journal of Archaeological Science 31 (2004) 799–814 SCIENCE Journal of Archaeological http://www.elsevier.com/locate/jas SCIENCE Journal of Archaeological http://www.elsevier.com/locate/jas 0305-4403/04/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jas.2003.10.016