Traffic
Hit
Also called collection event.
Hit is any single request the collector accepts. A pageview is a hit, but so is an event, a heartbeat or a form interaction.
How it is measured
Count every accepted collection request. Each hit carries a type, a timestamp, a page and sometimes parameters. Hit totals therefore grow with every event you add, even when the number of people does not.
Tarsier accepts pageview hits, custom event hits and engagement pings from the cookieless script. The pings keep duration and the Live view working and do not show up as extra pageviews, so raw hit volume will always exceed pageview volume.
Worked example
A newsletter signup page adds scroll tracking at 25, 50, 75 and 100 percent. Overnight the property's hits double from 18,000 to 36,000 while pageviews stay at 9,000.
The admin who budgets by hit volume is startled until she sees that the new events are the cause. Her quota is hit-based, so she moves the 25 percent mark to a sampled setting.
How it differs
A hit is the raw request. A pageview is one kind of hit. An event is another. A session is a group of hits. Counting hits as visits overstates traffic by the average events per visit.
Common errors
Using hits as a traffic measure. Reporting hits to a manager as visitors. Forgetting that bots and prefetches create hits. Letting event volume change a quota. Comparing hit totals across tools with different rules.
In practice
Use hits for capacity and billing. Use pageviews, sessions and visitors for audience. Before you add an event, estimate how many hits per visit it adds.