Population geography is a large branch of geography that contains several different topics related to the world's population. The first of these is population distribution, which is described as the study of where people live. World population is uneven as some places are considered rural and are sparsely populated, while others are more urban and are densely populated. Population geographers interested in population distribution often study past distributions of people to understand how and why specific areas have grown into large urban centers today. Usually, sparsely populated areas are harsh places to live such as Canada's northern territories, while densely populated areas like Europe or the coastal United States are more hospitable.
Closely related to population distribution is population density - another topic in population geography. Population density studies the average number of people in an area by dividing the number of people present by total area. Usually these numbers are given as persons per square kilometer or mile.
There are several factors which affect population density and these are often subjects of population geographers' study as well. Such factors can relate to the physical environment like climate and topography or be related to the social, economic and political environments of an area. For example, areas with harsh climates like California's Death Valley region are sparsely populated. By contrast, Tokyo and Singapore are densely populated because of their mild climates and their economic, social and political development.
Overall population growth and change is another area of importance for population geographers. This is because the world's population has grown dramatically over the last two centuries. To study this overall subject, population growth is looked at via natural increase. This studies an area's birth rates and death