Location-Based Social Networks Yu Zheng and Xing Xie Microsoft Research Asia Chapter 8 and 9 of the book Computing with Spatial Trajectories

Outline Chapter 8 (Location-based social networks: Users) – Concepts, definition, and research philosophy – Modeling user location history – Computing user similarity based on location history – Friend recommendation and community discovery Chapter 9 (Location-based social networks: Locations) – Generic travel recommendations Mining interesting locations and travel sequences Trip planning and itinerary recommendation Location-activity recommendation – Personalized travel recommendation User-based collaborative filtering Item-based collaborative filtering Open challenges

Social Networks “A social network is a social structure made up of individuals connected by one or more specific types of interdependency, such as friendship, common interests, and shared knowledge.” 3

Social Networking Services A social networking service builds on and reflects the real-life social networks among people through online platforms such as a website, providing ways for users to share ideas, activities, events, and interests over the Internet. 4

Locations Location-acquisition technologies Outdoor: GPS, GSM, CDMA, … Indoor: Wi-Fi, RFID, supersonic, … Representation of locations Absolute (latitude-longitude coordinates) Relative (100 meters north of the Space Needle) Symbolic (home, office, or shopping mall) Forms of locations Point locations Regions Trajectories 5

Locations + Social Networks Add a new dimension to social networks Geo-tagged user-generated media: texts, photos, and videos, etc. Recording location history of users Location is a new object in the network Bridging the gap between the virtual and physical worlds Sharing real-world experiences online Consume online information in the physical world 6

Examples 7 Physical world Virtual world Sharing & Understanding Generating & Consuming Interactions

Location-Based Social Networks 8 Sharing Understanding Sharing Geo-tagged media Virtual  Physical worlds Understanding User interests/preferences Location property User-user, location-location, user-location correlations Locations Social networks Locations An new dimension: Geo-tag An new object Social networks Expanding social structures Recommendations Users Locations media

Data + Intelligence Third Party Services Microsoft Services Scenarios - Sharing

Data + Intelligence Third Party Services Microsoft Services Data  Information  Knowledge  Intelligence Scenarios - Understanding

Location-Based Social Networks (LBSN) 11 not only mean adding a location to an existing social network so that people in the social structure can share location-embedded information, but also consists of the new social structure made up of individuals connected by the interdependency derived from their locations in the physical world as well as their location-tagged media content Here, the physical location consists of the instant location of an individual at a given timestamp and the location history that an individual has accumulated in a certain period. The interdependency includes not only that two persons co-occur in the same physical location or share similar location histories but also the knowledge, e.g., common interests, behavior, and activities, inferred from an individual’s location (history) and location-tagged data. From Book “Computing With Spatial Trajectories”

Categories of LBSN Services Geo-tagged-media-based Point-location-driven Trajectory-centric 12 Geo- LBSN ServicesFocusReal-timeInformation Geo-tagged-media-basedMediaNormalPoor Point-location-drivenPoint locationInstantNormal Trajectory-centricTrajectoryRelatively SlowRich

Locations Research Philosophy 13 User-Location Graph Users Trajectories User Graph User Correlation Location Graph Location Correlation Location-tagged user-generated content

Research Philosophy Sharing Making sense of the data Effective and efficient information retrieval …… 14

15 Repla y Shar e Replay travel experiences on a map with a GPS trajectory

16

Research Philosophy Understanding Understanding users Understanding locations Understanding events 17 User Graph Location Graph

Understanding Users (Chapter 8) 18 User similarity/ link prediction Experts/Influencers detection Community Discovery

Understanding Locations (Chapter 9) Generic recommendation Most interesting locations and travel routes/sequences Itinerary planning Location-activity recommenders Personalized recommendation Location recommendations User-based collaborative filtering model Item-based collaborative filtering model Open challenges 19

Understanding Events Anomaly Crowd Behavioral Patterns 20

Mining User Similarity Based on Location History 21

22 Grouping users in terms of the similarity between their location histories, and conduct personalized location recommendations. GIS ‘08/Trans. On the Web

23 GPS trajectories Geo-Location history User similarity Semantic Location history Model user location history Geographic spaces Semantic spaces Mining User Similarity Based on Location History

Computing user similarity Hierarchical properties Sequential properties Popularity of a location 24

3. Individual graph building 1. Stay point detection 2. Hierarchical clustering

Friend and Location Recommendation 26 Similar Users Retrieval User taste inferring L1, L2, …., Ln u1 u2. un x1, x2, …, xn y1, y2, …, yn. z1, z2, …, zn Location Candidates Discovering Ranking Locations

Mining interesting locations and travel sequences from GPS trajectories 27

28 Mining interesting locations, travel sequences, and travel experts from user-generated travel routes

29 Users: Hub nodes Locations: Authority nodes The HITS-based inference model

Location-Activity Recommendation

Goal: To Answer 2 Typical Questions 31 Q2: where should I go if I want to do something? (Location recommendation given activity query) Q1: what can I do there if I visit some place? (Activity recommendation given location query)

Problem Data sparseness ( <0.6% entries are filled) 32 Activities Locations 5?? ?1? 1?6 Forbidden City TourismExhibitionShopping Bird’s Nest Zhongguancun ?

Solution Collaborative filtering with collective matrix factorization – Low rank approximation, by minimizing where U, V and W are the low-dimensional representations for the locations, activities and location features, respectively. I is an indicatory matrix. 33

Locations Research Philosophy 34 User-Location Graph Users Trajectories User Graph User Correlation Location Graph Location Correlation Location-tagged user-generated content

New Challenges in LBSNs Heterogeneous networks Locations and users Geo-tagged media and trajectories Special properties Hierarchy / granularity Sequential property Fast evolving Easy to access a new location User experience/knowledge changes 35 Conferences Authors Papers Locations Users Media

GeoLife Trajectory Dataset (1.1) Version 1.0Version 1.1Incremental Time span of the collection04/2007 – 08/200904/2007 – 12/ months Number of users Number of trajectories15,85417,355+1,501 Number of points19,304,15322,294,2642,990,111 Total distance600,917 km1,070,406 km+469,489 km Total duration44,776 hour48,349 hour+3,573 hour Effective days8,9779, Transportation mode Distance (km) Duration (hour) Walk11,4575,126 Bike6,3352,304 Bus21,9311,430 Car & taxi34,1272,349 Train74, Airplane28,49337 Other10, Total187,67912,041

Link to the data

Conferences ACM SIGSPATIAL Workshop on Location-Based Social Networks LBSN 2011: Nov. 1, 2011, in Chicago (3 rd year) Over 40 attendees this year 26 submissions. 10 full papers and 4 short papers 38

Summary Locations and social networks Sharing and understanding New challenges and new opportunities 39

Thanks! 40 Yu Zheng