Explanation:

In the Census of India migration is enumerated on two bases

• place of birth, if the place of birth is different from the place of enumeration (known as life-time migrant);
• place of residence, if the place of last residence is different from the place of enumeration (known as migrant by place of last residence).
• As per 2001 census, out of 1,029 million people in the country, 307 million (30 per cent) were reported as migrants by place of birth. However, this figure was 315 million (31 per cent) in case of place of last residence. Over 45.58 crore Indians were found to be “migrants” for various reasons during the enumeration exercises of Census 2011. Census data shows that marriage and employment are the major reasons for migration.
• The Economic Survey 2016-17 used data from Census 2011, rail traffic data and changes in population in different age categories to estimate migration statistics. It estimates that an average of 90 million people migrated annually through railways between Indian statesannually during the last five years.
• Hence only place of birth and place of residence were used as bases for enumeration of migration.