Sessionization

Sessionization takes a raw clickstream of individual, timestamped events for a visitor and groups them into discrete visits, or sessions, so that "what did this person do in one sitting" becomes a countable unit rather than an undifferentiated stream. The result is the session records that most web and product analytics tools report on.

The most common method is a timeout rule: a new event starts a new session if it arrives more than a fixed gap, often 30 minutes, after the previous event from the same visitor. Some platforms also force a session boundary at midnight or on a change of campaign source. This differs from raw event counting, which has no notion of a visit at all, and from a login session, which is bounded by authentication rather than inactivity.

Sessionization matters because session-level metrics — session count, bounce rate, pages per session — are the basic units most web reporting is built from, and they feed user journey analytics that reconstruct paths within a visit. The main pitfall is timeout choice: a short timeout splits one real visit into several sessions, inflating session counts, while a long timeout merges genuinely separate visits, especially across devices or browser tabs left open in the background.