Recent years have seen active development of contextaware applications and systems that helps the development. However, it suffers from increasing fears for leakages of users' activity information to other users unconsciously, since the owner of the activity information included in the sensor data is not treated in context-aware systems. We propose the Area-Based Activity Information Preservation (ABAIP) system that enables users to control the level of data resolution of their activity information to allow applications to use. Degrading sensor data resolution causes coarse grained context recognition. The system prevents unconscious and unnecessary activity information leakage amongst the ABAIP system users, while providing ubiquitous sensor environment for various kinds of ubiquitous software.