Client queries regarding the definition of a visit and a unique visitor have become customary in my experience. Although their mere definitions are quite easy to comprehend, its their application and significance that leaves a lot to be pondered over. In this series we will try to explore how deep this rabbit hole really goes.

Defining a Visit

First of all, for those of us who are not well versed with analytics, a visit is NOT an individual. A visit is a session. A session that expires when:

• More than 30 minutes have elapsed between pageviews for a single visitor.
• At the end of a day.
• When any traffic source value for the user changes. Traffic source information includes:utm_source,utm_medium,utm_term,utm_content,utm_id,utm_campaign, andgclid.

source: http://analytics.blogspot.in/2011/08/update-to-sessions-in-google-analytics.html

I am sure you have a few questions here, such as:

What's end of day?
A. It's 12:00AM as per the timezone configured within your profile settings.

What happens when you come back from the same link within 30min?
A. The session does not expire as the traffic source information is not changing.

What happens when you close the browser?
A. The session does not expire. Closing the browser meant end of the visit earlier. But now this is no longer a factor with the deprecation of the _utmc cookie.

A more elaborate explanation on the definition of a visit (or session) can be found in this video by Avinash Kaushik.

Defining Unique Visitors

"Unique Visitors represents the number of unduplicated (counted only once) visitors to your website over the course of a specified time period. A Unique Visitor is determined using cookies." source: http://support.google.com/googleanalytics/bin/answer.py?hl=en&answer=33087

To put it simply, unique visitors are the number of unique individuals (i.e. browser clients to be more precise) that access your website over a given time period.

The time aspect of the definition is crucial for understanding this metric. It ought to be more clearer with the sample report illustrated below:

The screenshot details the visits and unique visitors coming to a website during the months of Dec '11, Jan '12 and Feb'12. At the first glance, there isn't anything extraordinary in the data being shown - we can see the total number of visits & unique visitors for individual months and the collective period. But if you look at it more closely, unique visitors don't quite add up:

The discrepancy is not an error but an indication of the time specific nature of unique visitors. Lets understand this with an example,

1. Consider a visitor (Bob) visiting the website thrice, once in Dec '11 and twice in Jan '12
2. For the overall period of Dec' 11 to Feb '12, the user has made one unique visit
3. However for the period of Dec '11 only, the user has made one unique visit
4. Similarly, for the individual period of Jan '12, the visitor has made one unique visit
5. Consequently, the sum of the unique visitors for the collective period will always be less than the unique visits made during the individual periods

Bob's visits to the website:

I hope this helps drive home the point that unique visitors is a time bound metric which will vary based on the time range that has been selected. In the subsequent part of the series we will explore considerations for conversions and new vs. returning visitors based on these fundamentals.

The post is written by Rohit Patil, Project Manager (Web Analytics) at Convonix. Get in touch with Rohit on Facebook and Google+. Feel free to ask your queries on @rohit_pro.