The document describes an ambient and multi-directional location-based mobile application called Heatmap that allows users to leave subjective impressions about places through ratings, text, photos, and audio. The application acts as an activity wayfinder and subjective guide for an area by filtering impressions based on a user's interests to provide a point of view of their locale. A prototype of Heatmap can be accessed online and it was developed for an iPhone conference by a team that includes people from Chicago, Germany, and the Philippines.