I was wondering why I was seeing such poor performance for ad impressions on my XForm unit conversion application. The application gets regular usage (which has been slowly climbing over time, now averaging 15 sessions per day, of about 1 minute per session), and while it is used globally, a lot of that usage comes from Canada, the US and the UK. However, I was seeing a paltry number of ads actually displayed when I checked on the iTunes Connect data (sorry, my agreement with Apple bars me from releasing actual numbers). We are talking less than 0.1%. Given that other apps were seeing enormous numbers of ads displayed, this didn’t seem right. So, after some digging, and a review of some of the sessions on iAds from WWDC, I believe I found my answer: I was requesting ads in both available sizes. Apparently, if you do this, you only get ads that have both available sizes, even if you only want to display one of them.
In iAds, you can request ads be either just 320×50 (for portrait-only apps), 480×50 (for landscape-only apps) or in both sizes. The iAds control will take care of displaying the appropriate ad when it arrives. By default, the iAd controller (the ADBannerView object) requests both sizes. It was mentioned at WWDC that if your app is only landscape or portrait, you should configure the control to only request the size that you want. Of course, in my excitement to get an iAd-enabled app on the iTunes App Store, I overlooked this little detail (and one that will now be part of my final deployment/submission checklist!), and requested both sizes, even though XForm only works in portrait orientation.
I submitted an update to the iTunes App Store to correct this issue, and now that the app has been for sale (and updated by nearly 100 people), my ad impression rate has jumped considerably. It appears that its still restricted to a small number of countries, but fortunately that does cover a big piece of my user base.
So remember: only select the ad size that you need for your app. If you don’t, you run the risk of having far fewer ads served to your app. As the base of available ads grows, and more and more are available in both sizes, this will be less of an issue. But until that happens, remember to pick the right ad size for your app.