Plains and Valleys are Densely Populated due to Soil Fertility
Explanation:
Plains and valleys are often densely populated due to their high soil fertility, which provides several advantages for human habitation and agricultural activities. Here are the reasons why this statement is true:
1. Favorable Soil Conditions: Plains and valleys typically have deep, fertile soils that are rich in nutrients. These soils are formed by the accumulation of sediment and organic matter over long periods, making them highly productive for agriculture.
2. Agricultural Opportunities: The fertile soil in plains and valleys creates favorable conditions for crop cultivation. The availability of nutrient-rich soil allows farmers to grow a wide variety of crops, leading to increased agricultural productivity and economic opportunities.
3. Water Availability: Plains and valleys are often located near rivers, streams, or underground water sources. This proximity to water bodies ensures a reliable water supply for irrigation, enhancing agricultural productivity and supporting larger populations.
4. Transportation and Infrastructure: The flat terrain of plains and valleys facilitates the construction of transportation networks such as roads, railways, and canals. These infrastructural developments not only enable the efficient movement of people and goods but also attract industries and businesses, leading to increased population density.
5. Settlement and Urbanization: The combination of fertile soil, water availability, and transportation networks makes plains and valleys ideal for human settlement. The presence of agriculture and economic opportunities in these areas attracts people, leading to the development of towns and cities with higher population densities.
In conclusion, the high soil fertility of plains and valleys provides favorable conditions for agriculture, which in turn attracts human settlement and leads to dense populations in these areas.

Explanation:

Soil Fertility:
- Plains and valleys are densely populated because of their high soil fertility.
- The soil in these areas is rich in nutrients and is suitable for agriculture.
- This fertile soil supports the growth of crops, making it easier for people to engage in farming activities.

Agricultural Productivity:
- The fertile soil in plains and valleys leads to high agricultural productivity.
- This, in turn, attracts people to settle in these areas as they can depend on agriculture for their livelihood.

Availability of Water:
- Plains and valleys often have access to water sources such as rivers and streams.
- This availability of water is crucial for agriculture and further contributes to the high population density in these areas.

Transportation and Communication:
- Plains and valleys generally have flat terrain, making it easier to build transportation networks such as roads and railways.
- This ease of transportation facilitates the movement of goods and people, further encouraging settlement in these areas.

Conclusion:
- In conclusion, the combination of soil fertility, agricultural productivity, availability of water, and efficient transportation networks makes plains and valleys attractive for human settlement, leading to high population density in these regions.