ga('send', 'pageview') bit. But how does that work?
A tracking pixel!
Placement in the DOM, you need not...
So a pretty interesting thing about tracking pixels, and anything in the browser really is that it doesn't actually need to be put on the page to exist in memory somewhere. In fact, even if that pixel is only 1x1 in size, it could bump something out of the way enough to trigger a repaint of the webpage, which might alert you to that pixel's existence, which is something that advertisers and their ilk stringently avoid.
So basically, that
ga('send', 'pageview') ends up generating a request to a server somewhere. That request looks like this
In the network tab of your devTools in your favorite browser you can break down all those query string params into something a little more interesting.
v:1 _v:j29 a:806595983 t:pageview _s:1 dl:http://www.ignoredbydinosaurs.com/2014/09/deconstructing-the-google-analytics-tag ul:en-us de:UTF-8 dt:Deconstructing the Google Analytics tag | Ignored by Dinosaurs sd:24-bit sr:1440x900 vp:1334x479 je:1 fl:15.0 r0 _u:MACAAAQAI~ jid: cid:1626931523.1412365384 tid:UA-8646459-1 z:962163205
Some of that stuff is understandable, some of it is not. But the point is that that request actually trigger a response of a 1x1 pixel.
# Response headers access-control-allow-origin:* age:66666 alternate-protocol:443:quic,p=0.01 cache-control:private, no-cache, no-cache=Set-Cookie, proxy-revalidate content-length:35 content-type:image/gif date:Fri, 03 Oct 2014 18:23:52 GMT expires:Mon, 07 Aug 1995 23:30:00 GMT last-modified:Sun, 17 May 1998 03:00:00 GMT pragma:no-cache server:Golfe2 status:200 OK version:HTTP/1.1 x-content-type-options:nosniff
If this were the first time I'd visited the internet, there would almost certainly be a set-cookie header in there as well, but since they set that cookie on me a LONG time ago, it doesn't get sent.
The kinda creepy thing is that since Google Analytics is on a large number of sites, and their origin servers are on the same domain (cookies), they can follow you around the internet from site to site to site in a way that nobody else can (save perhaps the other giant analytics providers, which probably have nowhere near the reach, unless you count Facebook).
Wow, cool. So what?
So that image pixel is not really the point. It gets returned in that response, but doesn't get put on the page. It plants a cookie on you, big deal.
But what happens at Google is that the request that was made in the first place gets logged. It gets broken down by its query string params, and that's how they build the tool. That's how you know what size browser people are on, what part of the world they're from, what they looked at, and what they clicked on (if you're tracking events).
The really interesting part to me, and the part I haven't figured out yet, is how they store ALL that data on the backend to build the reports out of. Think about it -- they're basically logging every request made to every website that is running their code. That's a really big number, even for Google. And then they're able to pull your report suite out of all that data, and sort it out by whatever you wanna know. Seems pretty cool, and also well beyond the capability of normal relational DBs.
A post in the future, I imagine....