You use the Internet all the time. Maybe you stream your favorite music, check out funny videos on YouTube, or share photos with friends on Instagram or Snapchat. But what is the Internet actually made of ? And when you type a password into a login screen or enter a search term into Google, where does it go? 

The Internet is a global network that allows us to connect with people anywhere. But it couldn’t exist without the vast network of cellphone towers, cables, and other structures that keep our vital communications humming. 

Some of these components are underwater or underground, while others are housed in buildings. “The Internet sometimes seems very abstract, but it depends on physical infrastructure to work,” says Paul Brodsky, an analyst at the telecommunications research company TeleGeography. “It’s an amazing combination of civil, electrical, marine, and computer engineering.”

Every year, Brodsky and his colleagues release a global map of the undersea cables that allow for high-speed communications across the world’s oceans. “Over 99 percent of long-distance communications today—web data, online videos, and even phone calls—travel through fiber-optic cables,” says Brodsky. 

Each fiber-optic cable contains strands of glass (see Inside a Cable). Data is converted into pulses of laser light that zip through the glass. Millions of miles of fiber-optic cable crisscross the U.S., allowing for high-speed data transmission across the country (see From You to YouTube).

The network of cables spanning the U.S. is a patchwork of infrastructure owned by many different companies. Computer scientist Paul Barford of the University of Wisconsin at Madison spent years gathering and double-checking maps of the most important equipment. Then he fused them together into a single map showing the backbone of the U.S. Internet. 

Internet infrastructure keeps our communications flowing, but it isn’t invincible. It’s vulnerable to threats like natural disasters or people trying to interfere with it. Barford’s map suggests ways to protect and strengthen our network. To keep connections working, says Barford, “you want to have different ways of getting from A to B, so that if one path is inaccessible, you have an alternate.” For example, the map shows that the East Coast has a dense network of infrastructure, but the central U.S. has much less. Additional cables there could strengthen the Internet in this region. 

New connections are being added all the time, both on land and at sea. Installing a cable at sea is a massive undertaking. It requires charting the safest possible route along the seafloor (avoiding areas prone to earthquakes and undersea volcanic eruptions) and then spooling out the cable from a ship. There are areas where it’s previously been impossible to lay cables—like across the Arctic Ocean, which is usually covered with ice for much of the year.

One project aims to take advantage of climate change. Melting sea ice in the Arctic has opened up a new passageway between Asia and Europe. A company called Arctic Fibre has proposed laying a new cable that would link Tokyo, Japan, and London, England. The link would shave time from communications between these two global financial centers—allowing data to travel one-way in just 154 milliseconds, as opposed to 178 milliseconds now—and also deliver the first fiber-optic Internet connections to communities in Alaska and northern Canada. “Bringing high-speed Internet to the Arctic for the first time would be a game changer,” says Arctic Fibre CEO Mike Cunningham.  

Barford hopes that as people learn more about how the Internet is built, they’ll be inspired to improve it: “When you find out how it works, you have an opportunity to make it better, faster, and more reliable.”