App downloads are on the rise and have recently topped 175 billion. Consequently, consumer spending exceeded $86 billion in 2017 alone and we have China, India, Russia, and Brazil to thank for this immense growth according to App Annie. In emerging markets such as these, it is encouraging to see such growth potential. China has long been a leader in the app download market, but is now followed by India which surpassed the United States, leaving it behind in third place.
Differences in Numbers
Where App Annie reported 175 billion downloads, Sensor Tower utilized its own analysis and showed 91.5 billion. The discrepancies come from how data is gathered. Sensor Tower draws form iOS App Store along with Google Play while App Annie also includes third party Android stores in the numbers. Google Play maintains little presence in China, thus the large difference between numbers. 
Growth for the Market
The country has seen a 215% increase over the past two years. That compares to a 125% growth spectrum in China. Unfortunately, the United States has seen a decrease in app downloads leading to a 5% drop in growth. Growth in India was largely increased due to subsidized, unlimited 4G access. Access granted by Jio in September 2016 gave way to waves of new customers downloading.
Growth Yet to Come
Among the mature markets in the world, the United States still maintains significant growth potential in volume of absolute downloads. App Annie found that users in the U.S. download 3 apps each month. 70% of those users download at least one app each month. It is also noted that comScore continually reports that in the U.S. users do not download any apps per month.
Engagement is Up as Well
Apps are not the only aspect of device use reported on. They have seen an increase in customer engagement as well. It is estimated that the average smartphone user maintains an average of 80 apps on their phone. These customers use at between one third and one half of the apps on their smartphones each month.
Increased Hours Spent on Smartphones
On average, consumers spent nearly 3 hours utilizing apps on smartphones daily. The study concluded that the numbers show a 30% increase in daily time spent on devices since 2015. Brazil, U.S. Russia, along with other markets have consumers spending up to 7x more time in mobile apps than on the web alone. They also access them 13 times more often.
Downloads in India has certainly seen a significant surge since the addition of the 4G network, however it has not seen a growth in consumer spending on apps. China leads here followed by the United States with India coming in third.
Consumer spending within app stores, including Google Play, iOS App Store, and third party Android stores has more than doubled in the past two years. At the end of 2017, those numbers topped out at $86 billion. Double digit growth potential can be seen in China leading the market at +270%. China is followed by Brazil +80%, the United States +75%, India +60%, and finally Russia at +35% in app spending. 
Projections for the Future
According to App Annie, app usage is only going to increase. They have recently forecasted that consumer app spending worldwide would top $110 billion by the end of 2018. The next five years are forecasted favourably as well with growth worldwide projected at 250 billion downloads by 2022. These numbers include China’s third-party Android downloads.
Growth projections have a drastic increase in smartphone base installs skyrocketing from 3.9 billion in 2017 to 6.1 gillion as of 2022. Those numbers show that almost everyone on the planet will have at least one device by 2022. 
Where is the Increase Occurring?
When speaking of download growth, it is not merely a matter of the number of increased smartphone users, but rather where those increases are taking place. First time smartphone buyers in emerging markets have a lot to do with app usage increase as well. Indonesia, Vietnam, Egypt, Brazil, Poland, Ukraine, and tier 3 cities in China are among the top growing first-time smartphone owner companies. These countries are not merely buying smartphones in increasing numbers, but utilizing apps at ever increasing rates as well. Within the next five years we are slated to see a drastic increase with the number of device installations bringing massive opportunity for publishers.
As those markets increase, publishers will have to step up to the plate and encourage new app downloads by innovating their current product to adapt to the needs of these emerging countries. High downloads along with limited direct spending will increase reliance on large base app publishers given them more of an impact in the global market. 
References https://www.appannie.com/en/insights/market-data/global-app-downloads-2017/  https://www.appmakr.com/blog/smartphone-usage-rise-developing-countries/  http://www.skywardtechno.com/blog/trends-shape-future-mobile-app-development/  https://www.strategyanalytics.com/zh/access-services/devices/mobile-phones/smartphone/smartphones/reports/report-detail/global-smartphone-sales-by-replacement-sales-vs.-sales-to-first-time-buyers-by-88-countries-2013—2022?slid=91630&spg=18&langredirect=true