What term describes the principle of dividing a country or province into constituencies based on population?

The principle described in the question is known as "representation by population." This concept asserts that electoral districts, or constituencies, should be created in a way that ensures each representative in a legislative body corresponds to approximately the same number of constituents. This method aims to provide a fair and equitable representation in government, reflecting the demographic composition of the population.

In a political context, representation by population seeks to ensure that people’s voices are heard equally, regardless of where they live. For instance, if one area has a significantly larger population than another, that area should have more representatives to maintain proportionality in governance.

The other terms do not apply to this specific principle. Social democracy refers to a political ideology that advocates for political democracy alongside social justice, focusing more on economic and social reform rather than the specific electoral processes of dividing constituencies. Equal voting generally pertains to the idea that each person's vote should carry the same weight, which is a broader concept that does not specifically address how constituencies are formed. A constituent assembly pertains to a body convened to draft or adopt a constitution, which is unrelated to the division of territory based on population.