As publisher, owner of a website it is important to optimize your website layout to maximize your ad revenue. Often a simple change in positioning or a different ad unit can have a disproportionate impact on the performance of the ads. How do you decide which position or ad unit works best? I have tried to answer that and more through this post. This post will help you decide by analyzing the ad units used in some of the top websites using a density map (which resembles a heat map). The methodology and formation of the density map is explained towards the end of the post.
Here is the density map...
On first observation you would notice that most ad units are clustered around the same locations. The brightness is directly proportional to the density of the ad units occurring in a certain location, which means more the ads, the more prominent it appears on the map. I have color coded the different ad units to help you differentiate one from the other; the 728x90 (leader board) ad units are represented by Cyan/Blue, 300x250 (medium rectangle) in Pink and 160x600 (wide skyscraper) in Orange.
The other ad units like the large rectangle, square ad unit aren't visible in the map because of low occurrence.
In my sample of websites, the top three ad units make up for nearly 90% of the allocation. To see the complete distribution of all ad units, refer to the pie chart below...
Here are my observations from the density map and the data compiled...
The leader board (728x90) is the most popular ad unit, followed by the medium rectangle (300x250) and the wide skyscraper (160x600).
Interestingly, leader board and medium rectangle are also the most paired appearing as a combination in over 40% of the websites sampled.
Convention suggests that greater the surface area of the ad unit, the more the visibility and hence a higher click-through rate (CTR). That justifies the popularity of the top three ad units in this sample but doesn't account for the large rectangle (336x280) which has a dismal 3% of the share. This can be explained by the fact that the Interactive Advertising Bureau (IAB) has de-listed this ad unit as they are no longer commonly bought/offered throughout the market.
As you can see from the density map, the most popular location for the leader board is at the top-centre of the website, besides the logo and above the navigation bar.
Similarly, the most popular location for the medium rectangle and the wide skyscraper (160x600) is near the top-left, below the navigation bar. This is the same for the square unit (250x250), large rectangle (336x280) and the half page ad (300x600)
When the medium rectangle and wide skyscraper are used together, the medium rectangle takes precedence usually positioned above the wide skyscraper.
The 728x15 (link unit) works best when it is placed closed to the navigation bar where it blends in well with the links. Some publishers have a link unit in place of the navigation bar.
Methodology for creating the density map...
For the density map, I gathered screenshots of 50 of the top websites in the world sourced from Alexa, Compete etc. Using a photo editing tool, I erased the content from the website screenshots leaving behind only the ads, layered them and decreased the opacity to 5%. The final merged layer was inverted (negative) to increase the contrast of the image.