Lazy loading is a technique used in ad servers to delay the loading of ads until they are close to appearing in a user's viewport (the visible area of the browser). Instead of loading all ads as soon as the page loads, lazy loading ensures ads are only served when a user scrolls to the appropriate section of the page. This approach is especially useful for pages with long content or multiple ads.

Why lazy loading is important

Improved page load speed — By only loading ads when they are needed, lazy loading reduces the initial load time of the webpage, resulting in faster page rendering and a better user experience.
Better viewability — Since ads are only loaded when they are about to come into view, lazy loading increases the likelihood of ads being seen by users, improving viewability metrics. auto_storiesViewability is crucial for advertisers, as it ensures that ads are actually seen, rather than buried out of sight.
Bandwidth efficiency — Lazy loading saves bandwidth by preventing unnecessary ad loads for users who may not scroll down the page. This is especially important on mobile devices, where conserving data is a priority.
Improved CTR — Ads below the viewable area of the page will never be seen if the user doesn't scroll down, negatively affecting CTR. By registering an impression when the ad is seen, CTR is improved naturally.

How lazy loading works

When a webpage with ads is loaded, placeholders for ads are initially displayed in locations where ads will eventually appear. It's the SPAN element in the auto_storiesad tag. As without lazy loading, ads are requested from the ad server, but simply not shown yet. As the user scrolls down the page, the browser detects when an ad slot is nearing the viewport. It sends a signal to the ad server, which then loads the ad on the page and registers an impression.

How to activate

Lazy loading is available for Display Ads only. To set this up, open a auto_storiesZone and navigate to the Settings tab. Toggle the 'Lazy Loading' box and you're ready to go.

Important

A few important things to notice:

Enabling lazy loading will not reduce the number of ad requests. Ads are still requested, but ad loading is deferred until the ad slot is in the viewport of the browser.
Lazy loading will reduce the number of impressions for ads below the viewport. After all, if the user doesn't scroll down, the ad won't load. CTR however will likely go to.
Ads are loaded when the placeholder is about 100 pixels below the browser's viewport, to ensure the ad is loaded when the user scrolls further down.

Conclusion

Lazy loading is a powerful feature in modern ad servers that optimizes ad delivery for publishers, advertisers and users. It improves page performance, increases ad viewability, reduces resource usage and improves CTR naturally. It's an important technique for delivering ads in a more user-friendly and efficient way, while increasing the quality of inventory offered to advertisers.

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