Multi Activity Recognition Based on Bodymodel-Derived Primitives.- Activity Inference through Sequence Alignment.- Improving Location Fingerprinting through Motion Detection and Asynchronous Interval Labeling.- Using Context Annotated Mobility Profiles to Recruit Data Collectors in Participatory Sensing.- Location Diversity: Enhanced Privacy Protection in Location Based Services.- Nonvisual, Distal Tracking of Mobile Remote Agents in Geosocial Interaction.- Directional Beaconing: A Robust WiFi Positioning Method Using Angle-of-Emission Information.- Bluetooth Tracking without Discoverability.- Error Estimation for Indoor 802.11 Location Fingerprinting.- Activity Recognition from Sparsely Labeled Data Using Multi-Instance Learning.- A Framework for Creating and Using Maps of Privately Owned Spaces.- Daily Routine Recognition through Activity Spotting.- SofTOA: Software Ranging for TOA-Based Positioning of WLAN Terminals.- Position Estimation from UWB Pseudorange and Angle-of-Arrival: A Comparison of Non-linear Regression and Kalman Filtering.- An Ultrasonic 3D Positioning System Using a Single Compact Receiver Unit.- LOCK: A Highly Accurate, Easy-to-Use Location-Based Access Control System.- Characterizing the Space by Presenting Non-visual Information.

These proceedings contain the papers presented at the 4th International S- posium on Location and Context Awareness (LoCA) during May 7-8, 2009 in Tokyo,Japan.Locationandcontextawarenessarefundamentstonext-generation mobile and pervasive computing systems. Pervasive computing is a model of computing in which computation is everywhere and computer functions are - tegrated into everything. The ultimate aim is to make information, applications and services available anywhere and at anytime in the human environment in a ?uid manner appropriate to our current context. Once away from the desktop, we ?nd ourselves in a wide variety of contexts and hence situations. For computing to be relevant and useful in these emerging situations we must rely on a range of contextual cues. Context includes phys- logical, environmental, and computational data, whether sensed or inferred. In addition, context includes details of a user's activities, goals, abilities, pref- ences, a?ordances, and surroundings. With location and context awareness we can expect computers to deliver information, services, and entertainment in a way that maximizes convenience and minimizes intrusion.