Adapted from eMarketer; Note: Forecast as of February 2019; Chart: Andrew Witherspoon/AxiosU.S. ad dollars spent this year on digital channels, including desktop, mobile, search, and social media, will surpass the total spent on non-digital ad channels, like television, out-of-home (billboards), radio, newspapers and magazines, according to a new projection from eMarketer.Why it matters: 2017 was the first year that digital ad spending passed the television ad spend in the U.S. Now, digital is growing so quickly that it's slated to surpass revenue from all of the old-school mediums that for decades dominated the entertainment landscape.Be smart: This is not surprising, given that out-of-home ads are the only traditional ad format that has been showing any real sign of growth over the past few years. It's also not surprising given that many of the older ad mediums are turning digital themselves, albeit slowly. The big takeaway: For the first time this year, the combined share of Google and Facebook's dominance of digital ads will actually drop, despite record revenues. That's because Amazon will continue to grow, eating at both companies' market share. eMarketer predicts that Amazon's U.S. ads business will grow more than 50% this year, putting Amazon on track to close the gap with Facebook, which is currently the second-biggest digital ad company by spend next to Google.