By Alexandra Olson, Associated Press

UNITED NATIONS (AP) — The number of people who migrated to foreign countries surged by 41 percent in the last 15 years to reach 244 million in 2015, according to a United Nations study released Tuesday. Of those people, 20 million are refugees. The U.N. is planning a series of meetings in 2016 to address migration, including a March 30 gathering in Geneva where countries can pledge to take in Syrians fleeing civil war. But while the Syrian refugee crisis has gripped the world's attention, it is but a drop in the sea of international migration.

Here are some highlights from the U.N. report on international migration:

—WHERE ARE MIGRANTS GOING?

By far, the United States is the country with the largest portion of the world's migrants: 47 million, or a fifth of the total. Germany and Russia shared the No. 2 spot with about 12 million each, followed by Saudi Arabia (10 million), Britain (9 million) and the United Arab Emirates (8 million.)

The vast majority of international migrants — two-thirds of the total — are in Europe or Asia. Europe is home to 76 million international migrants, while Asia has 75 million.

—WHERE ARE MIGRANTS COMING FROM?

While Asia and Europe host the largest portions of international migrants, they also contribute the most. Asia is the biggest regional source of international migrants, with 104 million, or 43 percent. Europe contributed 25 percent, or 62 million. The U.N. report explained that migration occurs mostly between countries located in the same region. Latin America and the Caribbean was the third-largest regional source of international migration, with 37 million, or 15 percent. Only 2 percent (4 million) are from North America.

India had the world's biggest diaspora, with 16 million people, followed by Mexico (12 million), Russia (11 million), China (10 million) and Bangladesh (7 million) and Pakistan and Ukraine (6 million each).

—WHO ARE THE MIGRANTS?

They are almost equally divided by gender: 48 percent are women. Not surprisingly, most are working-age. The median age of migrants in 2015 was 39. A significant portion — 15 percent — were under 20 years old. But country populations will not get any younger as a result. The United Nations said migrants can help ease old-age dependency ratios in some countries but will not halt the long-term trend toward population aging. All major areas of the world are still projected to have significantly higher old-age dependency ratios in 2050.

—WHAT DOES THIS MEAN FOR THE WORLD POPULATION?

The vast majority of the world's people stay put. Migrants made up just 3.3 percent of the global population in 2015, up from 2.8 percent 15 years ago. Still, international migration is growing faster than the world's population, with significant consequences for many regions.

Migrants make up 10 percent of the populations of Europe, North America and Oceania. In North America and Oceania, migrants have contributed to 42 percent of population growth since 2000. It was a different story in Europe, where the population would have declined over the same period had it not been for the influx of migrants. Even if current migration levels continue, Europe's population is still projected to decline over the next 35 years because of its surplus of deaths over births.

To Learn More:

More Mexican Immigrants Leaving U.S. than Entering … and Most are Leaving Voluntarily (by Noel Brinkerhoff, AllGov)

New Immigrants from China and India Now Outnumber Immigrants from Mexico (by Noel Brinkerhoff and Danny Biederman, AllGov)

U.S. Losing its Dominance as Mecca for Immigrants with College Degrees (by Noel Brinkerhoff and Danny Biederman, AllGov)

Largest Immigrant Groups in U.S.: Mexican, Filipino, Indian (by Noel Brinkerhoff, AllGov)