Hierarchical graphs and clustered graphs are useful non-classical graph models for structured relational information. Hierarchical graphs are graphs with layering structures; clustered graphs are graphs with recursive clustering structures. Both have applications in CASE tools, software visualization, and VLSI design. Drawing algorithms for hierarchical graphs have been well investigated. However, the problem of straight-line representation has not been solved completely. In this paper, we answer the question: does every planar hierarchical graph admit a planar straight-line hierarchical drawing? We present an algorithm that constructs such drawings in linear time. Also, we answer a basic question for clustered graphs, that is, does every planar clustered graph admit a planar straight-line drawing with clusters drawn as convex polygons? We provide a method for such drawings based on our algorithm for hierarchical graphs.

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A weakness of many interactive visual programming languages (VPLs) is their static representations. Lack of an adequate static representation places a heavy cognitive burden on a VPL s programmers, because they must remember potentially long dynamic sequences of screen displays in order to understand a previously written program. However, although this problem is widely acknowledged, research on how to design better static representations for interactive VPLs is still in its infancy. Building upon the cognitive dimensions developed for programming languages by cognitive psychologists Green and others, we have developed a set of concrete benchmarks for VPL designers to use when designing new static representations. These benchmarks provide design-time information that can be used to improve a VPL s static representation.

In this paper we report on our experiences with applying genetic algorithms to the drawing of undirected graphs with straight line edges. Since there exists a relatively simple but powerful heuristic for this class of graphs, namely the spring algorithm, we use this algorithm as a local fine-tuner within the genetic algorithm. We compare our results with drawings produced by the spring algorithm alone and discuss the strengths and weaknesses of the approach presented. Keywords: spring algorithm, evolutionary algorithm, genetic algorithm, graph drawing 1 Introduction The problem of drawing a graph nicely can be regarded as searching for an optimal layout of a given graph according to some measurable aesthetics. However, solving this problem to optimality seems to be computationally infeasible even for relatively simple aesthetic criteria [7], thus one is bound to the area of heuristics and stochastic search methods. In recent years, a lot of research on the problem to support the auto...

Visualization is an important aspect of both exploration and communication of categorical as well as relational data. Graphical displays of policy networks are particularly attractive, since they enable authors to display in a compact way relevant actors in a network, how they are related to each other, and what the overall structure looks like. Sociograms were early companions of social network analysis, but have received surprisingly little attention during the following decades. Only in the last few years, easy accessability of quality computing and graphic equipment has revived a now rapidly growing interest. In this paper, we analyze the problem of visualizing policy networks. We first argue why network visualization is important, yet non-trivial. Then, we show that current methods are somewhat ad hoc in their attempt to convey information contained in a network. Our main contribution is a systematic approach to network visualization, closely following the general principles of in...

UML class diagrams are helpful for understanding the structure of a software system. Algorithms and tools have been developed to generate UML class diagrams automatically for program understanding purposes. However, many tools often ignore perceptual factors in the layout of these diagrams. Therefore, users still have to spend much time and effort rearranging boxes and lines to make the diagram understandable. This paper presents key criteria and guidelines for the effective layout of UML class diagrams from the perspective of perceptual theories. Two UML tools have been analyzed and evaluated to illustrate how the criteria can be applied to improve the readability of class diagrams.

Abstract. In this paper we present a generic algorithm for drawing sequences of graphs. This algorithm works for different layout algorithms and related metrics and adjustment strategies. It differs from previous work on dynamic graph drawing in that it considers all graphs in the sequence (offline) instead of just the previous ones (online) when computing the layout for each graph of the sequence. We introduce several general adjustment strategies and give examples of these strategies in the context of force-directed graph layout. Finally some results from our first prototype implementation are discussed. 1

Abstract. This paper describes a within-subjects experiment in which we compare the relative effectiveness of five sociogram drawing conventions in communicating underlying network substance, based on user task performance and usability preference, in order to examine effects of different spatial layout formats on human sociogram perception. We also explore the impact of edge crossings, a widely accepted readability aesthetic. Subjective data were gathered based on the methodology of Purchase et al. [14]. Objective data were collected through an online system. We found that both edge crossings and conventions pose significant effects on user preference and task performance of finding groups, but either has little impact on the perception of actor status. On the other hand, the node positioning and angular resolution might be more important in perceiving actor status. In visualizing social networks, it is important to note that the techniques that are highly preferred by users do not necessarily lead to best task performance. 1

This paper describes a hybrid Genetic Algorithm (GA) that is used to improve the layout of a graph according to a number of aesthetic criteria. The GA incorporates spatial and topological information by operating directly with a graph based representation. Initial results show this to be a promising technique for positioning graph nodes on a surface and may form the basis of a more general approach for problems involving multi-criteria spatial optimisation. 1. Introduction and Background Many spatial problems have a common need to locate interacting objects on a surface. Applications as diverse as geographical data analysis and molecular modelling deal with location as a special feature within a vector of attributes that describe a problem. Generic GAs have been used in applications such as electronic engineering design problems [6]; molecular conformational analysis [13,14,]; network and graph optimisation [15,17]. These systems deal with a variety of graph based representations but...

This report is broken down into four main sections, firstly giving the primary aims of the proposed research, followed by a review of background reading of present Information Visualisation (IV) techniques, which are categorised using an existing framework. This is followed by a description of the general visualisation problem we are concerned with plus a description of the specific area where such a visualisation could be of benefit. We then discuss the visualisation techniques that address situations that have the greatest similarity to our own problem, and explain why they still lack suitability for our purposes. Then, two prototypes that are under development are described, and the report finishes with a breakdown of proposed future work