Spatio-temporal patterns of human mobility from geo-social networks for urban computing: Analysis, models & applications

The availability of rich information about fine-grained user mobility in urban environments from increasingly geographically-aware social networking services and the rapid development of machine learning applications greatly facilitate the investigation of urban issues. In this setting, urban computing emerges intending to tackle a variety of challenges faced by cities nowadays and to offer promising approaches to improving our living environment. Leveraging massive amounts of data from geo-social networks with unprecedented richness, we show how to devise novel algorithmic techniques to reveal underlying urban mobility patterns for better policy-making and more efficient mobile applications in this dissertation. Building upon the foundation of existing research efforts in urban computing field and basic machine learning techniques, in this dissertation, we propose a general framework of urban computing with geo-social network data and develop novel algorithms tailored for three urban computing tasks. We begin by exploring how the transition data recording human movements between urban venues from geo-social networks can be aggregated and utilised to detect spatio-temporal changes of local graphs in urban areas. We further explore how this can be used as a proxy to track and predict socio-economic deprivation changes as government financial effort is put in developing areas by supervised machine learning methods. We then study how to extract latent patterns from collective user-venue interactions with the help of a spatio-temporal aware topic modeling approach for the benefit of urban infrastructure planning. After that, we propose a model to detect the gap between user-side demand and venue-side supply levels for certain types of services in urban environments to suggest further policymaking and investment optimisation. Finally, we address a mobility prediction task, the application aim of which is to recommend new places to explore in the city for mobile users. To this end, we develop a deep learning framework that integrates memory network and topic modeling techniques. Extensive experiments indicate that the proposed architecture can enhance the prediction performance in various recommendation scenarios with high interpretability. All in all, the insights drawn and the techniques developed in this dissertation make a substantial step in addressing issues in cities and open the door to future possibilities in the promising urban computing area

Spatiotemporal user and place modelling on the geo-social web

Users of Location-Based Social Networks (LBSN) are giving away information about their whereabouts, and their interactions in the geographic space. In comparison to other types of personal data, location data are sensitive and can reveal user’s daily routines, activities, experiences and interests in the physical world. As a result, the user is facing an information overload that overburdens him to make a satisfied decision on where to go or what to do in a place. Thus, finding the matching places, users and content is one of the key challenges in LSBNs. This thesis investigates the different dimensions of data collected on LBSNs and proposes a user and place modelling framework. In particular, this thesis proposes a novel approach for the construction of different views of personal user profiles that reflect their interest in geographic places, and how they interact with geographic places. Three novel modelling frameworks are proposed, the static user model, the dynamic user model and the semantic place model. The static user model is a basic model that is used to represent the overall user interactions towards places. On the other hand, the dynamic user model captures the change of the user’s preferences over time. The semantic place model identifies user activities in places and models the relationships between places, users, implicit place types, and implicit activities. The proposed models demonstrate how geographic place characteristics as well as implicit user interactions in the physical space can further enrich the user profiles. The enrichment method proposed is a novel method that combines the semantic and the spatial influences into user profiles. Evaluation of the proposed methods is carried out using realistic data sets collected from the Foursquare LBSN. A new Location and content recommendation methods are designed and implemented to enhance existing location recommendation methods and results showed the usefulness of considering place semantics and the time dimension when the proposed user profiles in recommending locations and content. The thesis considers two further related problems; namely, the construction of dynamic place profiles and computing the similarity between users on LBSN. Dynamic place profiles are representations of geographic places through users’ interaction with the places. In comparison to static place models represented in gazetteers and map databases, these place profiles provide a dynamic view of how the places are used by actual people visiting and interacting with places on the LBSN. The different views of personal user profiles constructed within our framework are used for computing the similarity between users on the LBSN. Temporal user similarities on both the semantic and spatial levels are proposed and evaluated. Results of this work show the challenges and potential of the user data collected on LBSN

POI prediction based on user selection influences

TCC(graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Ciências da Computação.Tendo em vista a dificuldade de escolha gerada pela grande diversidade de estabelecimentos encontrados nas cidades atualmente e a crescente aderência da população a redes sociais baseadas em localização, realiza-se uma pesquisa aplicada exploratória quali-quantitativa com enfoque indutivo sobre os frameworks existentes de recomendação e de predição de pontos de interesse. Foram identificados 5 fatores que influenciam usuários de redes sociais baseadas em localização a visitarem novos estabelecimentos: geografia, tempo, amizade, personalidade e escolhas feitas por usuários similares. Baseado nesses frameworks e nas influências identificadas, desenvolve-se um modelo unificado que será capaz de prever que estabelecimentos cada usuário visitará com base em parte de sua trajetória individual. Para tanto, divide-se a trajetória de cada usuário em duas partes, a primeira para análise e a segunda para validação, de modo que, ao aplicar o modelo desenvolvido à primeira parte da trajetória, idealmente chega-se na segunda. O modelo é aplicado à base de dados da rede social Gowalla. Diante disso, verifica-se que dentre os 5 fatores identificados, a escolha de usuários similares e a amizade obtiveram a melhor acurácia, e a união dos 5 fatores apresentou resultados melhores que cada fator individualmente, porém, diferentemente dos outros frameworks estudados, a melhora não foi significativa, o que impõe a constatação de que o problema precisa ser estudado mais a fundo.Taking into account the difficulty of choice generated by the great diversity of points of interest currently found in cities and the population increasing adherence to location-based social networks, a qualitative and quantitative exploratory applied research with inductive reasoning is performed on existing points of interest prediction and recommendation. 5 factors that influence users from location-based social networks to visit new points of interest were identified: geography, time, friendship, personal taste and choices made from similar users. Based on the identified influences and the frameworks, an unified model that is capable of predict what points of interest each user will visit based on their individual trajectory is developed. To validate the model, each user trajectory is divided in two parts, the first for analysis and the second for validation, so that by applying the developed model to the former, ideally the latter is achieved. Finally, the model is applied to a Gowalla social network dataset. Facing the results, it is stated that among the five influential factors identified (geography, time, friendship, personal taste and similarity with other users), the similarity with other users and the friendship achieved the best prediction accuracy, and the unified model presented better results than each factor individually, however, unlike the other studied frameworks, the improvement was negligible, which imposes that the problem needs further research

Context and Semantic Aware Location Privacy

With ever-increasing computational power, and improved sensing and communication capabilities, smart devices have altered and enhanced the way we process, perceive and interact with information. Personal and contextual data is tracked and stored extensively on these devices and, oftentimes, ubiquitously sent to online service providers. This routine is proving to be quite privacy-invasive, since these service providers mine the data they collect in order to infer more and more personal information about users. Protecting privacy in the rise of mobile applications is a critical challenge. The continuous tracking of users with location- and time-stamps expose their private lives at an alarming level. Location traces can be used to infer intimate aspects of users' lives such as interests, political orientation, religious beliefs, and even more. Traditional approaches to protecting privacy fail to meet users' expectations due to simplistic adversary models and the lack of a multi-dimensional awareness. In this thesis, the development of privacy-protection approaches is pushed further by (i) adapting to concrete adversary capabilities and (ii) investigating the threat of strong adversaries that exploit location semantics. We first study user mobility and spatio-temporal correlations in continuous disclosure scenarios (e.g., sensing applications), where the more frequently a user discloses her location, the more difficult it becomes to protect. To counter this threat, we develop adversary- and mobility-aware privacy protection mechanisms that aim to minimize an adversary's exploitation of user mobility. We demonstrate that a privacy protection mechanism must actively evaluate privacy risks in order to adapt its protection parameters. We further develop an Android library that provides on-device location privacy evaluation and enables any location-based application to support privacy-preserving services. We also implement an adversary-aware protection mechanism in this library with semantic-based privacy settings. Furthermore, we study the effects of an adversary that exploits location semantics in order to strengthen his attacks on user traces. Such extensive information is available to an adversary via maps of points of interest, but also from users themselves. Typically, users of online social networks want to announce their whereabouts to their circles. They do so mostly, if not always, by sharing the type of their location along with the geographical coordinates. We formalize this setting and by using Bayesian inference show that if location semantics of traces is disclosed, users' privacy levels drop considerably. Moreover, we study the time-of-day information and its relation to location semantics. We reveal that an adversary can breach privacy further by exploiting time-dependency of semantics. We implement and evaluate a sensitivity-aware protection mechanism in this setting as well. The battle for privacy requires social awareness and will to win. However, the slow progress on the front of law and regulations pushes the need for technological solutions. This thesis concludes that we have a long way to cover in order to establish privacy-enhancing technologies in our age of information. Our findings opens up new venues for a more expeditious understanding of privacy risks and thus their prevention

Recommending places blased on the wisdom-of-the-crowd

The collective opinion of a great number of users, popularly known as wisdom of the crowd, has been seen as powerful tool for solving problems. As suggested by Surowiecki in his books [134], large groups of people are now considered smarter than an elite few, regardless of how brilliant at solving problems or coming to wise decisions they are. This phenomenon together with the availability of a huge amount of data on the Web has propitiated the development of solutions which employ the wisdom-of-the-crowd to solve a variety of problems in different domains, such as recommender systems [128], social networks [100] and combinatorial problems [152, 151]. The vast majority of data on the Web has been generated in the last few years by billions of users around the globe using their mobile devices and web applications, mainly on social networks. This information carries astonishing details of daily activities ranging from urban mobility and tourism behavior, to emotions and interests. The largest social network nowadays is Facebook, which in December 2015 had incredible 1.31 billion mobile active users, 4.5 billion “likes” generated daily. In addition, every 60 seconds 510 comments are posted, 293, 000 statuses are updated, and 136,000 photos are uploaded1. This flood of data has brought great opportunities to discover individual and collective preferences, and use this information to offer services to meet people’s needs, such as recommending relevant and interesting items (e.g. news, places, movies). Furthermore, it is now possible to exploit the experiences of groups of people as a collective behavior so as to augment the experience of other. This latter illustrates the important scenario where the discovery of collective behavioral patterns, the wisdom-of-the-crowd, may enrich the experience of individual users. In this light, this thesis has the objective of taking advantage of the wisdom of the crowd in order to better understand human mobility behavior so as to achieve the final purpose of supporting users (e.g. people) by providing intelligent and effective recommendations. We accomplish this objective by following three main lines of investigation as discussed below. In the first line of investigation we conduct a study of human mobility using the wisdom-of- the-crowd, culminating in the development of an analytical framework that offers a methodology to understand how the points of interest (PoIs) in a city are related to each other on the basis of the displacement of people. We experimented our methodology by using the PoI network topology to identify new classes of points of interest based on visiting patterns, spatial displacement from one PoI to another as well as popularity of the PoIs. Important relationships between PoIs are mined by discovering communities (groups) of PoIs that are closely related to each other based on user movements, where different analytical metrics are proposed to better understand such a perspective. The second line of investigation exploits the wisdom-of-the-crowd collected through user-generated content to recommend itineraries in tourist cities. To this end, we propose an unsupervised framework, called TripBuilder, that leverages large collections of Flickr photos, as the wisdom-of- the-crowd, and points of interest from Wikipedia in order to support tourists in planning their visits to the cities. We extensively experimented our framework using real data, thus demonstrating the effectiveness and efficiency of the proposal. Based on the theoretical framework, we designed and developed a platform encompassing the main features required to create personalized sightseeing tours. This platform has received significant interest within the research community, since it is recognized as crucial to understand the needs of tourists when they are planning a visit to a new city. Consequently this led to outstanding scientific results. In the third line of investigation, we exploit the wisdom-of-the-crowd to leverage recommendations of groups of people (e.g. friends) who can enjoy an item (e.g. restaurant) together. We propose GroupFinder to address the novel user-item group formation problem aimed at recommending the best group of friends for a pair. The proposal combines user-item relevance information with the user’s social network (ego network), while trying to balance the satisfaction of all the members of the group for the item with the intra-group relationships. Algorithmic solutions are proposed and experimented in the location-based recommendation domain by using four publicly available Location-Based Social Network (LBSN) datasets, showing that our solution is effective and outperforms strong baselines

Advanced Location-Based Technologies and Services

Since the publication of the first edition in 2004, advances in mobile devices, positioning sensors, WiFi fingerprinting, and wireless communications, among others, have paved the way for developing new and advanced location-based services (LBSs). This second edition provides up-to-date information on LBSs, including WiFi fingerprinting, mobile computing, geospatial clouds, geospatial data mining, location privacy, and location-based social networking. It also includes new chapters on application areas such as LBSs for public health, indoor navigation, and advertising. In addition, the chapter on remote sensing has been revised to address advancements

Location Data: Perils, Profits, Promise

Most of the modern online economy is based on websites offering free services and content in exchange for advertising access and user data. Web companies collect vast troves of data about their users in order to better target their advertisements. An important subset of this harvested data is the locations visited by users. Location data is valuable as it is a ``real world" signal compared to online behaviors: a visit to a store is a stronger signal than a visit to a website, and location data can reveal user attributes that are interesting to advertisers. The collection of this data, however, raises many concerns. Location data can reveal important attributes that users may not wish to disclose: ZIP codes can reveal income and race, visits to places of worship may allow discrimination, and insurers may want to know about trips to hospitals. The risks exist at both an individual level, with location tied to physical safety, and at a collective level, with inference about group membership a necessary step towards discrimination. In this thesis, I examine issues of privacy and fairness in the use of location data. In the first portion, I empirically demonstrate new attacks on the anonymity and privacy of users, including a theoretical basis for user identification. In the second portion, I propose and analyze new solutions for dealing with privacy, anonymity, and fairness in the collection and use of location data. In contrast to previous work which presents privacy in abstract ways or ignores the power of data aggregators, the work presented here focuses on concretely informing users and incorporates the economic incentives driving privacy and fairness concerns

Museums, Social Media, and the Fog of Community

In the early twenty-first century, museums increasingly turn to "social media" to engage audiences and in these efforts they routinely imagine them as "communities." This dissertation tends to the politics of that choice, which extends a long history of museums employing community as a strategy towards institutional reform. Museums invoke community in numerous ways but without typically articulating those meanings, even though they influence the implementation and evaluation of social media projects. I argue that this lack of articulation creates a "fog" over practices--an ambiguous and confusing context of work--in which community operates as a "self-evident good," but serves traditional interests as much as transformative ones. To expose the many ideas that lay within this fog, I examine how American museums invoked community throughout the last century, showing how they use it both to reinforce their power and alter relations with audiences. After exploring how community has been conceptualized through networked digital media and social media--technologies and a culture that emphasize openness, communication, collaboration, and the materialization of digital bodies--I show how museums continue to use community in complex ways. As social media conflate community with communication--specifically "face-to-face," or immediate, communication, I argue they influence museums to over-value visible acts of communication, which narrows their understanding of online visitor engagement and dilutes the potential of community to shape projects that more conscientiously serve audiences and institutional reform. To illustrate the complexity of these ideas at work, I present three case studies of museums using social media to construct community: the Getty Center's blog, A Different Lens; the Japanese American National Museum's website, Discover Nikkei; and the website of the Science Museum of Minnesota's Science Buzz. I expose the definitions of community at work in each, examine how they influence the use of media, and work to limit and serve the project's various democratizing goals. The conclusion offers a nascent problematique that suggests more critical approaches museums may take for invoking community and using social media towards democratizing aims

Social informatics

5th International Conference, SocInfo 2013, Kyoto, Japan, November 25-27, 2013, Proceedings</p