Apple is set to hold its annual Worldwide Developers Conference (WWDC) next week, and there have been plenty of speculations regarding what we can expect. Some are expecting to see a new Apple Pay reward program introduced, while others are looking for a TV streaming service.

WWDC 2015 Preview: What Apple Developers Should Know

The unveiling of iOS 9 is pretty much a guarantee, as the latest iOS version is always the main event at WWDC each year.

App industry growing rapidly

But what about new apps? Along with iOS 9 will come updates to apps and also entirely new apps. After all, developers attend WWDC to learn about the latest version of iOS so that they can build apps around it. ACT/ The App Association has published its latest report entitled “WWDC Preview: The iOS App Economy,” which focuses on expected app trends at WWDC this year.

This is the seventh year the app marketplace has really been in existence, and it’s been growing rapidly. It’s estimated that this year 800,000 new developers will join the app. Within the next two years, it’s expected that the app market will bring $150 billion in annual revenue. (All images in this article are courtesy ACT/ The App Association.)

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The Apple Watch became available for purchase in April, so unsurprisingly, developers are busily churning out apps for it. In conducting its analysis, ACT looked at the top 400 apps in the most popular categories in Apple’s App Store.

Apple Watch apps front and center at WWDC

One of the trends the firm noted was that already 40% of the top health apps integrate with the Apple Watch. Further, the apps that quickly added integration with the smartwatch suddenly became among the most popular on iOS.

One of the most popular apps that integrates with the Apple Watch is Dark Sky, a weather app that alerts Apple Watch wearers about rain and snow. After becoming available on the Apple Watch, the app was the most-downloaded app on iOS for six days in a row, and the developer enjoyed soaring revenue.

Another popular app is WaterMinder, which is mainly targeted at athletes, nursing mothers and kidney patients. It helps users stay hydrated by monitoring the amount of water they take in. According to ACT, WaterMinder’s download ranking skyrocketed, climbing from 297th to land within the top ten on the Apple App Store—but it took integration with the Apple Watch to get iOS users interested.

Finance App Chronicle-Bill Reminders saw a similar phenomenon, as it leaped into the top rankings of the finance category after adding support for the Apple Watch. According to the ACT, more than a third of the top-ranked apps have now added support for the Apple Watch.

Clearly this is something developers will have to take into consideration while at WWDC if they haven’t integrated their apps with the Apple Watch yet.

Getting to the top of the heap

The organization discovered that 40% of the apps that support the Apple Watch are in the health category, while 34% fall into weather and 20% are in finance.

Further, it learned that in terms of geography, the App Store is quite diverse. U.S. developers contribute the lion’s share of the top apps at 80%, although just a few are in Silicon Valley, interestingly, as 77% of the top developers are located elsewhere.

When the first iPhone was introduced in 2007, Apple started with 500 preapproved apps. After one year, the company opened the App Store to third-party developers. ACT credits this move with allowing developers to focus entirely on writing code, thus causing “a blistering pace of innovation.”

The organization noted that in order to earn a spot among the top-ranking apps, developers must constantly update features. It’s too easy for newcomers to enter the App Store with a blockbuster app that steals users.

WWDC an incubator for new developers?

One of the main reasons Apple holds WWDC is to encourage app development for iOS, and a surprisingly large percentage of developers that ranked the top of ACT’s survey didn’t rank at all in previous reports. Overall, more than 32% of this year’s top-ranking developers were unknown a year ago. Here’s a breakdown by category: