The usual track of a page impression is fairly clear and simply: put the code at the end of the page.
But with the growing use of in-page changes to layout and content, when is it OK to log a new page impression and when would it considered to by just an record of an event?
My understanding is that page impression have a strong relationship to ad impressions (at least that's what I understand from my surrounding colleagues).
When I've a page which reveals completely new content to the user without having to reload (everything is already pre-loaded for performance matter), can this be considered a page impression? If so, then it would not relate to the PI/AI math anymore and looks troublesome to me.
Should I rather track that as kind of click event, properly named, but not being calculated to the totals of page impressions?
Some of those user interaction do only simple things like activating a feature for something (e.g. subscribe to a thread, in-application bookmark). I wouldn't call them a new page impression, but an event.
Page impression may be overrated but it's still used as a unit of measure every now and then. Unique users number are as important, too. This question is not about PI vs. Unique user/clients/whatever, but strictly related on how to handle such events.