How do states divide the number of constituents in their congressional districts?

By Population

Explanation:

Congressional districts refers to the electoral districts of a country responsible for electing one member of the district to represent the particular districts at the congress of the concerned country. It is practiced in countries such as Japan and United States

Division of constituents of a state into congressional districts is strictly based on population,

For instance, the United States House of Representatives has 435 congressional districts of which a single congressional district represent 747,000 people. Several districts within a state have same population and are separated by borders.

The 2012 United States Election was the first election to be based on the Congressional Districts in the US, using 2010 census data.