1) Where is the world's population distributed?

        As shown above, different countries have different density population, even thought they are within the same continent. China, India, Indonesia, and Japan are some of the highly populated countries in Asia. If the arithmetic density of Japan was to be taken, the number of people in Japan would be far greater than Japan’s total land area. While continents like Europe have many countries that are highly dense, Africa consists of countries where some have high density and some have low density. Not every country in Africa is overpopulated. As shown in the picture above, the density of Botswana is lower than Israel while the density of Nigeria is greater than the density of the United States. The United States is considered an overpopulated globalized nation, meaning it interacts worldwide economically, technologically, politically, and culturally. This being said, the five most populated countries in the world are China with 19.5% of the worlds population, India with 17.3%, United States with 4.52%, Indonesia with 3.46%, and Brazil with 2.82%.
 For an article link-  http://www.telegraph.co.uk/news/newstopics/politics/2967374/England-is-most-crowded-country-in-Europe.html

 2) Where has the world’s population increased?

Population Increase from 1950 to 2050

                Just 50 years ago, the world population was around 3 billion, and today, the estimated world population has dramatically increased to 6.8 billion. The population of a country is found by the crude birth rate (CBR), crude death rate (CDR), immigration, and emigration. The natural increase rate of the world is increasing exponentially. Many countries in America, Europe, and some parts of Asia have access to medicine. In 1950, the United States had a population of about 151 million, and in 2010, the estimated population is around 309 million. This is not because of high fertility rate, but it is due to low death rate, and immigration. On the other hand, many parts of Africa have a high total fertility rate due to farming reasons or because they do not use family planning methods. The world’s population has increased in every country; however, it has increased at different rates for different countries.
For a video link- http://www.youtube.com/watch?v=4BKQiQyaYc

      3) Why is population increasing at different rates in different countries?

                   Each country has its own rate of population increase. Through a population pyramid, we can see a countries population broken down to male and female, and then it is divided in to age groups.

                                                                             The first pyramid shown is the population pyramid of USA, consisting around 309 million people, is expected to increase steadily. The second pyramid is the population pyramid of Japan, consisting around 125 million people, has a lot of elderly citizens and not as many children. In the future, Japan's dependency ratio will decrease because there will not be enough middle aged working people. The third pyramid is the population pyramid of Ethiopia, consisting around 82 million people. Ethiopia has a lot of young people and little elderly citizens meaning its population is increasing rapidly. By 2050 Ethiopia is expected to have a population of 171 million people. The reason why different countries are increasing at different rates is because the countries are at different transitions.  

                     The transitions are broken down in to different stages as shown above. Stage 1 has high birth rate and high death rate. Stage 2 has high birth rate and low death rate due to the medical revolution. Stage 3 has low birth rate, because people begin to under stand how expensive children are, and low death rate. Stage 4 also has a low birth rate and low death rate. The 5^th Stage is when the natural increase changes to natural decrease because the birth rate is lower than the death rate; which means, there is zero population growth. Since countries are categorized in different stages, there will be different population increase rates.
For a video link- http://www.youtube.com/watch?v=PfGLJwiYTE8

 4)Why might the world face an over population problem?

                     If the natural increase of people is increasing faster than the production of food supply, the people will face starvation. Towards the late 1700s, Thomas Malthus believed that by the 1800s, people will face starvation and famine because there will not be enough food to feed everyone. However, his prediction was incorrect because the industrial revolution increased the supply of food which was able to feed the population. Malthus believed the poor should not be helped, and people need to have self control when it comes to having babies. Alternative ideas came from Karl Marx. Karl Marx believed that the solution for poverty was socialism or communism. He thought that capitalism leads to destruction, and it separates classes between the rich and the poor. This being said, overpopulation problem might occur if the population increase is higher than the food supply   production. 

For an article link- http://www.articlebase.com/environment-articles/overpopulation-thebiggest-threat-to-our-planets-survival-520631.html