In demographic terminology, what is meant by the "density of population" for a country or region?

Introduction / Context:
This question comes from basic demography and geography. The concept of population density is used to compare how crowded or sparsely populated different regions are. It is a standard measure reported in census reports, geography textbooks, and economic surveys. Understanding this definition is crucial for interpreting maps, charts, and statistics related to population distribution.

Given Data / Assumptions:
The question asks what is meant by density of population and lists several possible interpretations:
- Ratio of people living below the poverty line to total population
- Number of persons living per square kilometre
- Number of persons in a city
- Number of persons living per kilometre of road length
It is assumed that the learner knows that population density is a spatial concept, relating the number of people to the area they occupy, usually in square kilometres for national and regional statistics.

Concept / Approach:
Population density is formally defined as the number of people per unit area. For most countries, the conventional unit is the number of persons per square kilometre. This ratio gives a simple measure of how tightly people are packed within that area. It does not focus on poverty ratios, city population counts alone, or people per road kilometre. Therefore, the correct approach is to select the option that explicitly mentions persons per square kilometre as the meaning of density of population.

Step-by-Step Solution:
Step 1: Recall that density of population is a measure that combines population and area. Step 2: Recognise that national and state level reports usually express density as persons per square kilometre. Step 3: Review the options and identify the one that directly states number of persons living per square kilometre. Step 4: Confirm that this matches the standard demographic definition used in census data and geography books. Step 5: Select number of persons living per square kilometre as the correct answer.

Verification / Alternative check:
To verify, consider common statistics such as India's population density being described as a certain number of persons per square kilometre in census reports. Similar figures are reported for other countries, comparing how densely or sparsely populated they are. Poverty ratios use different measures, such as percentage of people below a poverty line, not persons per unit area. City population counts give absolute numbers rather than density unless divided by the area. People per kilometre of road length is a separate indicator related to infrastructure, not demographic density. These comparisons confirm that population density is correctly defined by persons per square kilometre.

Why Other Options Are Wrong:
Ratio of people living below the poverty line to total population: This measures poverty, not how many people live in a given area.
Number of persons in a city: This tells the size of the city's population but not how that population is distributed over land area.
Number of persons living per kilometre of road length: This relates population to road infrastructure and is not the standard demographic measure of density.

Common Pitfalls:
Learners sometimes confuse different kinds of ratios used in social science. They may pick the poverty ratio because it also involves a numerator and denominator, or they may think of city population without considering area. To avoid such mistakes, always associate density with people per unit area and recall that square kilometre is the standard unit for country and state level density in most official statistics.

Final Answer:
Density of population is defined as the number of persons living per square kilometre of area.