Harrison White and several anonymous reviewers for valuable comments on the work. We argue that social networks can be modeled as the outcome of processes that occur in overlapping local regions of the network, termed local social neighborhoods. Each neighborhood is conceived as a possible site of interaction and corresponds to a subset of possible network ties. In this paper, we discuss hypotheses about the form of these neighborhoods, and we present two new and theoretically plausible ways in which neighborhood-based models for networks can be constructed. In the first, we introduce the notion of a setting structure, a directly hypothesized (or observed) set of exogenous constraints on possible neighborhood forms. In the second, we propose higher-order neighborhoods that are generated, in part, by the outcome of interactive network processes themselves. Applications of both approaches to model construction are presented, and the developments are considered within a general conceptual framework of locale for social networks. We show how assumptions about neighborhoods can be cast within a hierarchy of increasingly complex models; these models represent a progressively greater capacity for network processes to “reach ” across a network through long cycles or semi-paths. We argue that this class of models holds new promise for the development of empirically plausible models for networks and network-based processes. 2 1.

While questions about social cohesion lie at the core of our discipline, definitions are often vague and difficult to operationalize. We link research on social cohesion and social embeddedness by developing a conception of structural cohesion based on network nodeconnectivity. Structural cohesion is defined as the minimum number of actors who, if removed from a group, would disconnect the group. A structural dimension of embeddedness can then be defined through the hierarchical nesting of these cohesive structures. We demonstrate the empirical applicability of our conception of nestedness in two dramatically different substantive settings and discuss additional theoretical implications with reference to a wide array of substantive fields. "...social solidarity is a wholly moral phenomenon which by itself is not amenable to exact observation and especially not to measurement." (Durkheim, (1893 [1984], p.24) "The social structure [of the dyad] rests immediately on the one and on the other of the two, and the secession of either would destroy the whole. ... As soon, however, as there is a sociation of three, a group continues to exist even in case one of the members drops out." (Simmel (1908 [1950], p. 123)

This article describes the structure of the adolescent romantic and sexual network in a population of over 800 adolescents residing in a midsized town in the midwestern United States. Precise images and measures of network structure are derived from reports of relationships that occurred over a period of 18 months between 1993 and 1995. The study offers a comparison of the structural characteristics of the observed network to simulated networks conditioned on the distribution of ties; the observed structure reveals networks characterized by longer contact chains and fewer cycles than expected. This article identifies the micromechanisms that generate networks with structural features similar to the observed network. Implications for disease transmission dynamics and social policy are explored.

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While questions about social cohesion lie at the core of our discipline, no clear definition of cohesion exists. We present a definition of social cohesion based on network connectivity that leads to an operationalization of social embeddedness. We define cohesiveness as the minimum number of actors who, if removed from a group, would disconnect the group. This definition generates hierarchically nested groups, where highly cohesive groups are embedded within less cohesive groups. We discuss the theoretical implications of this definition and demonstrate the empirical applicability of our conception of nestedness by testing the predicted correlates of our cohesion measure within high school friendship and interlocking directorate networks. Keywords: Social networks, social theory, social cohesion, connectivity algorithm, embeddedness. "...social solidarity is a wholly moral phenomenon which by itself is not amenable to exact observation and especially not to measurement." (Durkheim, (1893 [1984], p.24) "The social structure [of the dyad] rests immediately on the one and on the other of the two, and the secession of either would destroy the whole. ... As soon, however, as there is a sociation of three, a group continues to exist even in case one of the members drops out." (Simmel (1908 [1950], p. 123)

This paper identifies an important paradigm shift in social research on HIV transmission, drug abuse, and risk reduction research. The article describes the key research trends and the institutional support for social network analysis in the HIV and drug risk field for the past decade. Key hypotheses and recommended areas for future research are identified.

We would like to thank Russ Bernard and two anonymous reviewers whose helpful comments on a previous draft of this paper have improved its clarity and focus. 1 In this paper, we explore the use of graph layout algorithms (GLAs) for visualizing proximity matrices such as obtained in cultural domain analysis. Traditionally, multidimensional scaling (MDS) has been used for this purpose. We compare the two approaches in order to identify conditions when each approach is effective. As might be expected, we find that MDS shines when the data are of low dimensionality and are compatible with the defining characteristics of Euclidean distances, such as symmetry and triangle inequality constraints. However, when working with data that do not fit meet these criteria, GLAs do a better job of communicating the structure of the data. In addition, GLAs lend themselves to interactive use, which can yield a deeper and more accurate understanding of the data. 2

In this article, the authors explore the use of graph layout algorithms for visualizing proximity matrices such as those obtained in cultural domain analysis. Traditionally, multidimensional scaling has been used for this purpose. The authors compare the two approaches to identify conditions when each approach is effective. As might be expected, they find that multidimensional scaling shines when the data are of low dimensionality and are compatible with the defining characteristics of Euclidean distances, such as symmetry and triangle inequality constraints. However, when one is working with data that do not fit these criteria, graph layout algorithms do a better job of communicating the structure of the data. In addition, graph layout algorithms lend themselves to interactive use, which can yield a deeper and more accurate understanding of the data. Keywords: multidimensional scaling; visualization; social network analysis; graph layout algorithms; cultural domain analysis; proximity matrices Visualization of proximity matrices is commonly used in cultural domain

This monograph is based on the papers from a technical review on “Social Networks, Drug Abuse, and HIV Transmission ” held on August 19-20, 1993. The review meeting was sponsored by the National

CONNECTIONS is the official journal of the International Network for Social Network Analysis (INSNA). INSNA is a scientific organization made up of scholars across the world. Updated information about the INSNA’s annual conference (Sunbelt Social Network Conferences) can be found on the website at www.insna.org. CONNECTIONS publishes original empirical, theoretical, and methodological articles, as well as critical reviews dealing with applications of social network analysis. The research spans many disciplines and domains including Anthropology, Sociology,