Migrants tend to move to countries neighbouring or close by their home countries.
LONDON — There were 244 million international migrants recorded in 2015, and over 60% of global migration consists of people moving to neighbouring countries or countries in the same region, according to the World Economic Forum (WEF).
Asia-to-Asia was the largest regional migration corridor in 2015, with 59 million migrants, followed by the Europe-to-Europe corridor, which had 40 million migrants.
According to the WEF, migrants contributed between $6.4 trillion and $6.9 trillion, or 9.4%, of the world's gross domestic product in 2015.
In 2016, the National Academies of Sciences, Engineering and Medicine found that although first generation immigrants are more costly to governments that the native born population, second generation adults are among the population's strongest economic and fiscal contributors.
Keep scrolling for some of the world's busiest migration routes:
The Mediterranean
The Central Mediterranean route was under intense pressure in 2015, although pressure eased slightly from 2014 as more Syrians moved to use the Eastern Mediterranean route and smugglers faced a shortage of boats.
Between January and November 2017, there were an estimated 116,573 illegal border crossings via this route.
Most migrants gather in Libya before making the rest of the journey by sea — typically in poorly equipped or old boats that are prone to capsizing.
There were also an estimated 19,808 illegal border crossings via the Western Mediterranean route between January and November 2017.
Source: Frontex
Eastern Mediterranean route
In 2015, 17 times the number of migrants arrived in the EU via the Eastern Mediterranean route than had done in 2014. The majority arrived on Greek islands, mainly Lesbos.
Between January and November 2017, there were an estimated 37,961 illegal border crossings via this route.
Most of the migrants on this route in 2015 originated from Syria, followed by Afghanistan and Somalia.
Source: Frontex
Central America
Migrants in Latin America generally move from rural to urban areas. The region has experienced considerable internal displacement over the last century, particularly Colombia at the moment.
Source: World Economic Forum
India
The interstate migration rate in India doubled between 2001 and 2011 compared to the previous decade, growing 4.5% annually and averaging between 5 and 6 million migrants per year.
This is driven by the states' economic inequalities: Bihar, which has one of the highest outflows of domestic migrants, has a per-capita income roughly equivalent to Somalia's (approximately $520) and a birth rate of 3.4 children per woman.
Kerald, a popular destination for migrants, has a per-capita income of roughly $2,350 and a birth rate of 1.6 children per woman.
Source: World Economic Forum
China
Over the past 30 years, the proportion of China's population living in urban areas has increased from 22.9% to 56.8% of its current 1.3 billion citizens.
The World Bank estimates that 1 billion people, or over 75% of the country's population, will be living in cities by 2030.
According to a survey by the National Bureau of Statistics of China, in 2012 China had more than 262 million internal migrant workers, which is more than the total number of international migrants worldwide.
Source: World Economic Forum
Russia
Russia has the third highest number of migrants in the world, third only to the United States and Germany. In 2015, this was estimated to be about 12 million, or about 8% of the population.
A high number of Russians are also internal migrants and resettle in another part of Russia.
Since 1990, some data on migration has been artificially inflated by statistics gathered in new countries formerly in the Soviet Union and former Yugoslavia, resulting in the classification of many people as migrants even if they have not moved. For example, over 2 million Russians currently living in Kazakhstan are classified as international migrants.
Source: World Economic Forum
Western African route
The route between Senegal, Mauritania and Morocco and the Spanish Canary Islands was once the busiest irregular entry point for all of Europe, with 31,600 arriving on the Islands in 2006, according to the European Border and Coast Guard Agency.
However, between January and October only 251 illegal border crossings were recorded.
Most migrants using this route arrived by sea in long wooden fishing boats.
Source: Frontex
Eastern routes
The European Border and Coast Guard Agency estimated between January and November 2017, there were 10,983 illegal border crossings via the Western Balkan route.
It estimated there were 5,696 illegal border crossings via the Circular route from Albania to Greece between January and October 2017.
Source: Frontex