(a) Movement to another country is emigration and movement into a country is immigration. Net migration is the difference between emigration and immigration.
(b) The economic effects of rural to urban migration.
(i) It increases the level of urban unemployment because of the rural-urban drift
(ii) Agriculture (food production) is reduced since the youths actively involve in agriculture move to urban areas.
(iii) Population explosion in cities increases the demand for social services like hospital, school, electricity, etc.
(iv) It leads to social problems such as homelessness, immorality, armed robbery which disrupt economic activities.
(v) Uneven distribution in population causes business activities to concentrate in urban centres.
(vi) The migrants provide cheap labour for the factories and other organizations in the urban centres.