As you might know, sponsored advertisements are one of the things that are funding The Polyglot Developer and everything it accomplishes, so keeping sponsors happy and supplying them the metrics they need is very important. However, in most circumstances, more specifically when it comes to banner creatives, page views is not enough. For example if your sponsors or potential sponsors asked how many impressions each of your advertisement zones gets, you can’t just list off the page views that those particular pages get because how do you know if the user actually saw the advertisement?
I’ve heard a few names when it comes to element impressions. Some call it element or image visibility, and some call it viewability. It doesn’t really matter as they are both trying to determine if the user has actually seen the image or element on their screen.