Scrolling down the page is recorded as a Google Analytics event.
By default we record 25/50/75/100 % scroll depth.
If page sections have their specific IDs, we can record web section names (IDs).
An example article from https://en.wikipedia.org/wiki/Google_Analytics
Google Analytics is a freemium web analytics service offered by Google that tracks and reports website traffic.Google launched the service in November 2005 after acquiring Urchin. Google Analytics is now the most widely used web analytics service on the Internet. Google Analytics is offered also in two additional versions: a subscription based Google Analytics Premium targeted at enterprise users and Google Analytics for Mobile Apps, an SDK that allows gathering usage data from iOS and Android Apps.
Google acquired Urchin Software Corp. in April 2005. Google's service was developed from Urchin on Demand. The system also brings ideas from Adaptive Path, whose product, Measure Map, was acquired and used in the redesign of Google Analytics in 2006. Google continued to sell the standalone, installable Urchin WebAnalytics Software through a network of value-added resellers until discontinuation on March 28, 2012.
The Google-branded version was rolled out in November 2005 to anyone who wished to sign up. However, due to extremely high demand for the service, new sign-ups were suspended only a week later. As capacity was added to the system, Google began using a lottery-type invitation-code model. Prior to August 2006 Google was sending out batches of invitation codes as server availability permitted; since mid-August 2006 the service has been fully available to all users – whether they use Google for advertising or not.
The newer version of Google Analytics tracking code is known as the asynchronous tracking code, which Google claims is significantly more sensitive and accurate, and is able to track even very short activities on the website. The previous version delayed page loading and so, for performance reasons, it was generally placed just before the </body> body close HTML tag. The new code can be placed between the <head>...</head> HTML head tags because, once triggered, it runs in parallel with page loading.
In April 2011 Google announced the availability of a new version of Google Analytics featuring multiple dashboards, more custom report options, and a new interface design. This version was later updated with some other features such as real-time analytics and goal flow charts.
In October 2012 the latest version of Google Analytics was announced, called 'Universal Analytics'. The key differences from the previous versions were: cross-platform tracking, flexible tracking code to collect data from any device, and the introduction of custom dimensions and custom metrics 
Integrated with AdWords, users can now review online campaigns by tracking landing page quality and conversions (goals). Goals might include sales, lead generation, viewing a specific page, or downloading a particular file.
Google Analytics' approach is to show high-level, dashboard-type data for the casual user, and more in-depth data further into the report set. Google Analytics analysis can identify poorly performing pages with techniques such as funnel visualization, where visitors came from (referrers), how long they stayed and their geographical position. It also provides more advanced features, including custom visitor segmentation.
A user can have 100 site profiles. Each profile generally corresponds to one website. It is limited to sites which have a traffic of fewer than 5 million pageviews per month (roughly 2 pageviews per second), unless the site is linked to an AdWords campaign.
Google Analytics Cohort analysis feature helps understand the behavior of component groups of users apart from your user population. It is very much beneficial to marketers and analysts for successful implementation of Marketing Strategy
In addition to transmitting information to a Google server, the tracking code sets a first party cookie (If cookies are enabled in the browser) on each visitor's computer. This cookie store anonymous information, called the ClientId. Before the launch of Universal Analytics, there were several cookies storing information such as whether the visitor had been to the site before (new or returning visitor), the timestamp of the current visit, and the referrer site or campaign that directed the visitor to the page (e.g., search engine, keywords, banner, or email).
If the visitor arrived at the site by clicking on a link tagged with Urchin Traffic Monitor (UTM) codes such as:http://toWebsite.com?utm_source=fromWebsite&utm_medium=bannerAd&utm_campaign=fundraiser2012
the tag values are passed to the database too.
In addition, Google Analytics for Mobile Package allows Google Analytics to be applied to mobile websites. The Mobile Package contains server-side tracking codes that use PHP, JavaServer Pages, ASP.NET, or Perl for its server-side language.
Another limitation of Google Analytics for large websites is the use of sampling in the generation of many of its reports. To reduce the load on their servers and to provide users with a relatively quick response for their query, Google Analytics limits reports to 500,000 randomly sampled sessions at the profile level for its calculations. While margins of error are indicated for the visits metric, margins of error are not provided for any other metrics in the Google Analytics reports. For small segments of data, the margin of error can be very large.
Google has also released a browser plugin that turns off data about a page visit being sent to Google. Since this plug-in is produced and distributed by Google itself, it has met much discussion and criticism. Furthermore, the realisation of Google scripts tracking user behaviours has spawned the production of multiple, often open-source, browser plug-ins to reject tracking cookies. These plug-ins offer the user a choice, whether to allow Google Analytics (for example) to track his/her activities. However, partially because of new European privacy laws, most modern browsers allow users to reject tracking cookies, though Flash cookies can be a separate problem again.
It has been anecdotally reported that behind proxy servers and multiple firewalls that errors can occur changing time stamps and registering invalid searches.
Webmasters who seek to mitigate Google Analytics specific privacy issues can employ a number of alternatives having their backends hosted on their own machines. Until its discontinuation, an example of such a product was Urchin WebAnalytics Software from Google itself.
On Jan. 20, 2015, the Associated Press reported in an article titled: "Government health care website quietly sharing personal data" that HealthCare.gov is providing access to enrollees personal data to private companies that specialize in advertising. Google Analytics was mentioned in that article.
Google offers free Google Analytics IQ Lessons, Google Analytics certification test, free Help Center FAQ and Google Groups forum for official Google Analytics product support. New product features are announced on the Google Analytics Blog. Enterprise support is provided through Google Analytics Certified Partners.sscsc
The Google Analytics API is used by third parties to build custom applications such as reporting tools. Many such applications exist. One was built to run oniOS (Apple) devices and is featured in Apple's app store. There are some third party products that also provide Google Analytic based tracking.
Google describes the limits and quotas for the Management API, Core Reporting API, MCF Reporting API, and Real Time Reporting API in case you are planning to use it for the marketing campaigns.
Google Analytics is the most widely used website statistics service, currently in use on around 55% of the 10,000 most popular websites. Another market share analysis claims that Google Analytics is used at around 49.95% of the top 1,000,000 websites (as currently ranked by Alexa).
Google Analytics is used by 66.2% of the 10,000 most popular websites ordered by popularity, as reported by BuiltWith in August, 2013. In May 2008, Pingdomreleased a survey stating that 161 (or 32%) out of 500 biggest sites globally according to their Alexa rank were using Google Analytics.