National income is the sum of the incomes of the owners of the production factors, belonging to a specific nationality and during a specific period of time.
It doesn't include income generated by production factors that belong to foreigners, and it does include income generated abroad by nationals.
The value of the national income is the same as the national product.
As a measure of welfare, national income doesn't take into account environmental pollution and income distribution.
Data Visualization: National Income Per Cápita per Country
Source: World Bank
See also: Meaning of GDP