distribution

Distribution refers to the way something is spread out or arranged over a geographic area. The concept of distribution can be applied to nearly everything on Earth, from animal and plant species, to disease infections, weather patterns, and man-made structures.
Many of the things geographers study are found in some places, but not in the others. This means these patterns occur in certain distributions over the Earth's surface. Geographers look for and try to explain any patterns that may occur. "Distribution" refers to the way something is spread out or arranged over an area. Recognizing distributions on a map is a starting point for many geographic studies. Geographers look for and try to explain any patterns that may occur.
Some distributions can be seen visually. The number of barns in a farming community can be seen from an airplane, for example.
Visual information is not always accurate or available, however. Areas may be too big to see, and some areas are not visible at all. These patterns of distribution need to be put on a map. World population is a good example of information that has to be mapped. Geographers can’t count the number of people in an area from the air. They rely on many types of information, such as census data, to determine the distribution of people in a certain area.
To understand distribution patterns, it is important to understand other factors, such as climate, landforms, and vegetation. For example, the human population distribution shows very few people living in Asia’s arid Gobi Desert. The desert offers few resources important for survival.
Conflict and economy can also influence distribution patterns. Thousands of Iraqi citizens left their country after the Iraq War began in 2003. Population distribution shows many Iraqis now living in Syria and Jordan.
The poor economy in rural areas of China have led millions of people to seek employment in huge urban areas such as Beijing and Shanghai. Working in factories and the service industry (hotels, restaurants) is often more profitable than farming. The distribution of rural and urban populations in China has become much more dramatic as a result.
Distribution is the way something is spread out over an area—it does not tell geographers why or how it is spread out.
One topic doctors and biologists study is distribution of the disease malaria. Malaria is found mainly in parts of the world that are tropical and humid. Malaria is common in these areas because the mosquitoes that carry and transmit the disease thrive in hot, humid climates. The distribution of human malarial infections shows high concentrations in tropical regions, and low concentrations in non-tropical regions.

‏Source www.nationalgeographic.org