Showing papers on "Visibility graph analysis published in 2019"

Visibility graph analysis of economy policy uncertainty indices

Abstract: Uncertainty plays an important role in the global economy. In this paper, the economic policy uncertainty (EPU) indices of the United States and China are selected as the proxy variable corresponding to the uncertainty of national economic policy. By adopting the visibility graph algorithm, the four economic policy uncertainty indices of the United States and China are mapped into complex networks, and the topological properties of the corresponding networks are studied. The Hurst exponents of all the four indices are within 0 . 5 , 1 , which implies that the economic policy uncertainty is persistent. The degree distributions of the EPU networks have power-law tails and thus the networks are scale-free. The average clustering coefficients of the four EPU networks are high and close to each other, while these networks exhibit weak assortative mixing. We also find that the EPU network in United States based on daily data shows the small-world feature since the average shortest path length increases logarithmically with the network size such that L N = 0 . 626 ln N + 0 . 405 . Our research highlights the possibility to study the EPU from the view angle of complex networks.

Dissecting Visibility Graph Analysis: The metrics and their role in understanding workplace human behaviour

Abstract: Visibility Graph Analysis (VGA) is one of the main methods of analysis of interior space within the field of Space Syntax, formulated by Turner et al. (2001) by extending Benedikt’s work on isovists and isovist fields (1979). It is a means to quantify the configuration of space as regular units which can then be used to identify the relationship of that space to the behaviour of the humans that occupy it. This paper is interested in the application of this method and its related metrics in workplaces, and how it can be used to understand the behaviour of office workers. Such information can then be used as evidence when designing new office spaces. We focus on the main tool used by the Space Syntax community: depthmapX (previously known as Depthmap). There are 25 VGA metrics that depthmapX can currently calculate, a mixture of classic graph-theory metrics, metrics borrowed from the urban-scale Space Syntax theories and some VGA-specific metrics describing local spatial properties. Some of the metrics are also derivatives, permutations and normalisations of other metrics which provide new information in relation to the configuration of space. While some of the metrics were described in previous research, there has never been a comprehensive understanding of all the VGA metrics produced by depthmapX, especially the concepts, formulae and algorithms behind their calculation. This has led researchers to focus on small subsets of these metrics avoiding thus the scattered and opaque nature of the theory and application. In previous research we have used VGA extensively aiming to understand human behaviour in office spaces but specifically only explored those that deal with local and global visibility. This paper first describes and elaborates on the various metrics produced by the current version of depthmapX and also outlines the theoretical considerations for each metric and how these potentially relate to human behaviour. Using a large dataset with VGA and observation data in office spaces we examine how these metrics relate to two kinds of behaviours: movement and interaction. We test how well each metric predicts each behaviour using two aggregations, per-floor and per-metric-quantile-bin. We show that for most of the metrics tested, permetric-quartile-bin works better than per-floor. The findings suggest that of the two behaviours examined, movement is best predicted, with many of the local and global metrics significant and with high effects. This paper contributes to the general Space Syntax field in relation to indoor spatial analysis, by providing a thorough description of the metrics of VGA. It also aims to highlight how and which of these metrics can be used to specifically understand human behaviour in workplaces. Ultimately, such information can be used to predict this behaviour in newly designed office-spaces and thus allow designers to inform their designs.

Three-dimensional visibility graph analysis and its application

Abstract: Graph-based visibility analysis, developed from space syntax and social network theory, embraces mutual visibility between locations in a spatial system. It helps designers and researchers to decode spatial cognition and behavior, but methodological constraints limit its application to two-dimensional floor plans. In this study, we propose a new visibility graph analysis that can be used in three-dimensional built environments, such as multilevel atrium buildings or urban environments with canopies or overpass bridges. Furthermore, we draw a distinction between a generic visibility graph and a targeted visibility graph. In the former, an occupiable location is considered as both the origin and target of visibility lines. In the latter, we further take into account the visible space or specific targets in a system. Visible locations are spaces people can see but cannot necessarily physically occupy. With this differentiation, the visibility graph system is more amenable to new applications in three-dimensi...

Multiscale Horizontal Visibility Graph Analysis of Higher-Order Moments for Estimating Statistical Dependency

Abstract: The horizontal visibility graph is not only a powerful tool for the analysis of complex systems, but also a promising way to analyze time series. In this paper, we present an approach to measure the nonlinear interactions between a non-stationary time series based on the horizontal visibility graph. We describe how a horizontal visibility graph may be calculated based on second-order and third-order statistical moments. We compare the new methods with the first-order measure, and then give examples including stock markets and aero-engine performance parameters. These analyses suggest that measures derived from the horizontal visibility graph may be of particular relevance to the growing interest in quantifying the information exchange between time series.

Detect and evaluate dependencies between aero-engine gas path system variables based on multiscale horizontal visibility graph analysis

Abstract: Identifying the interaction in aero-engine gas path system is a crucial problem that facilitates the understanding of emerging structures in the complex system. By employing the multiscale horizontal visibility graph method to aero-engine gas path system, the interaction characteristics between gas path system parameters are established. Comparing with normalized mutual information method, the advantage of the multiscale horizontal visibility graph method in detecting interaction is showed. And then, the effect of time scale s on the multiscale horizontal visibility graph analysis is investigated. The results show that the multiscale horizontal visibility graph method is effective to detect the interaction of gas path system parameters.

Agent based simulation for 'Choice of Seats': a Study on the Human Space Usage Pattern

Abstract: Agent simulation in the context of architecture is a great practical tool for analysing space and examining its influence from the perspective of users. On the other hand, the theories and concepts that deal with human cognition as it relates to environments are typically studied within the field of environmental psychology. Research on the intersection between the two fields has focused mainly on the analysis of the built environment but not necessarily the agents themselves. The present research applies the theories in environmental psychology as rules in an agent simulation model validated by comparing the results with actual mapped human behavioural patterns in space. It aims to develop a method and a tool for analysing space from the perspective of the users and thus allow for the design of built environments that take that perspective into account. We specifically used visibility graphs to map the visitors’ field of view on spatial configurations as a proxy for the concepts of “prospect and refuge” in environmental psychology. We then applied an agent model to the same spatial configurations that simulated the tendency to prefer sitting areas that are a certain distance from others and as well as other elements of human cognition such as the perception of crowdedness of a space and uncertainty. We validated the simulation model against onsite observations to examine how the hypothetical patterns it creates relate to the observed patterns in real-world settings in the context of the theories implemented from environmental psychology. No statistically significant correlations emerged between the theoretical patterns and observed behaviour pointing to the complexity of human usage patterns in space as well as the difficulties of measuring it. Nevertheless, the proposed research provides a framework for investigating people’s possible staying patterns over spatial configurations and seat arrangements with different concordant rates according to crowdedness conditions and group type.

The Morphology of Public Open Spaces as Visual Opportunity Fields - A space syntax approach based on Revelation and VGA maps customization with SalaScript

Abstract: This paper explores the visual dynamics of the morphology of public open spaces. Resorting to space syntax concepts, visual graph analysis (VGA), and the innovative use of its standard tool Depthmap, a set of case studies is analysed under the perspective of visual opportunity fields and building upon the established concept and metrics of Revelation. A series of related novel measures and visualizations are developed, which are only possible, in Depthmap environment, by the advanced use of its scripting language: SalaScript. Despite Depthmap being the standard tool among the space syntax community, there is a lack of references to the explicit use of SalaScript. One major objective of this paper is to illustrate, and document, its possibilities to a broad audience by extending, customizing and introducing a more interactive approach in handling VGA maps. We present SalaScript functionalities and its use in the development of visual analysis scripts that allow the study of revelation, which we then apply to a set of real public open spaces case studies.

Visibility graph analysis

Abstract: The visibility graph analysis (VGA) is a method based on “graph theory techniques” and represents an alternative and radically different tool for the analysis of time series. The method was introduced in the literature in 2008 by Lacasa et al. [1] . In short, a visibility graph can be obtained by mapping a time series into an associated complex network, allowing the use of the powerful tools of complex network theory in the tasks of signal processing and signal analysis. Several studies suggest that such a network inherits in its topology the series information and hidden structure. A complex network description can thereby fully characterize the time series and the underlying dynamical process that generated such a series from a relatively novel angle [2] .

Measuring visibility to urban functions with social media data

Abstract: Urban public space is not only characterised by the connection of visible spaces, but also featured by the visible functions, thereby forming the different spatial atmosphere that humans can interpret. In this article, public spaces are conceptualised as a set of viewsheds/ isovists that are further used to generate visibility graph (VG) of mutual visibility between spatial locations and functional places. By adding land-use locations into the visibility graph, the current Visibility Graph Analysis (VGA) measures in the space syntax model can be extended to form a novel approach to investigate the fine-scaled spatio-functional interactions though public space in the dense built environment. In so doing, a framework called ‘Function Visibility Graph Analysis (FVGA) is introduced, in which a series of measures are introduced to reflect various respects of viable landscape. The public spaces are further grouped to function spaces, for describing the functional identity for urban spaces with reference to the compositions of the visibility for various types of functions. All these measures of the graph are accomplished of comparing location to location within a system, comparing systems with different spatial layouts or land-use patterns. It is shown that FVGA can be effective to assess the feasibility of detail urban design and land-use allocations.

Ambiance through Spatial Organization in Vernacular architecture of hot and dry regions of India − The case of Ahmedabad and Jodhpur

Abstract: Most notable vernacular settlements of the past had a potential of generating stimulating ambiance because of their “organicness”. The understanding of the “Nature of order” in this informality can identify the factors or parameters generating the definite spatial character appropriate for the time and place. The spatial character generates the spirit of the place, what we call the genius loci. This paper analyses the relationship of spatial organization and ambiance of the old city settlements in hot and dry climatic regions of two selected cities of India − Ahmedabad and Jodhpur at various levels. Both the selected cities are informal in nature and rich with its ambiance. Space syntax and digital simulations are used to decode the parameters of the spatial organization. The spatial morphology is analysed using tools such as justified graph analysis, visibility graph analysis, isovists analysis, agent movement analysis and sunlight study. The result of the study is summarised in tabular format and presented in a graphical manner for better understanding. This analysis is valuable in the derivation of the constants and variables to define the learning from the vernacular spatial organization.