In the very beginning, all countries were at the same level of development. However, some countries started to develop faster than the others because of presence of natural resources or good natural harbour. this has resulted in some countries to become the core countries{ Developed countries; DCs } the lack of job opportunities in the Periphery countries { less developed countries; LDCs } has result in more and more people moving from the LDCs to the DCs in search of job opportunities. this movement of labour drained the workfore in the LDCs. On the other hand, the DCs are are benefiting from the additional talent in their countries which generates more wealth. The core countries continues to develop in the expense of the periphery countries. this effect is known as the backwash effect. however, since the 1990s, DCs realised that the cost of setting up manufacturing industries is lower in the LDCs. this has resulted in many companies setting up manufactories in LDCs. with more companies setting up manufactories in the LDCs, there are more job opportunities in the LDCs. the LDCs are now benefitting from the growth of the DCs. this effect is known as the spread effect. this also resulted in some countries to become the secondary core countries. the region is fully intergrated with more periphery countries benefitting from the core countries and inequalities are reduced to some extent.

GDP refers to the total amount of money generated by a country in a year.
GDP per capita refers to the average income a person is earning in a country.
GDP per capita= total amount of money generated in a country in a year divided by the total number of people in a country.

HDI stands for Human development Index. It is an index used by the United nation development programme to measure the level of development in a country. the closer the HDI is to 1, the more developed a country is. the further the HDI is from 1, the less developed a country is.

To measure HDI, there are many indicators. three main catagories: Health indicators, Education indicators and economic indicators.

Economic indicators:
(i)Employment structure
-in a country, different people work in different industries. there are three main industries: primary, secondary and tertiary. primary industries includes farming and plantation agriculture. secondary industries refers to manufacturing industires. and tertiary industries refers to the service industry.
-with a greater percentage of people working in the secondary and tertiary industry{ higher paying jobs}& a smaller percentage of people working in the primary industry, the greater the income per capita in the country. more and more people are able to afford better goods and services which leads to a better standard of living and a better quality of life.

(ii) job opportunies
- with more job opportunities in a country, more and more people would be employed in various industries which would contribute to the countries's GDP. more and more people would be able to afford goods and services and this will leads to a higher standard of living and better quality of life.

Health Indicators:
(iii) Life expectancy
the life expectancy refers to the amount of years a person is expected to live. in more developed countries, the life expectancy rate would be higher as there are clean water, food and better health care services.

(iv) Infant mortallity rate
the infant mortallity rate refers to the number of babies that are less than the age of 1, dies for every 1000 live babies. in more developed countries, the infant mortallity rate would be low as there is good healthcare services.

(v)Availibility of clean water supply
-water is essential for our survival as well as to carry out certain activities such as cooking, drinking and manufactoring.
-in developed countries like japan or norway, the people have better access to clean water supply as water is supplied to their homes by pipes. before the water is sent to these homes, the water is first sent to water treatment facilities to be treated to ensure that all bacteria and impurities are removed.
-On the other hand, in less developed countries, there is little access to clean water supply. the people usually have to walk long distances to collect water from a well as they cannot affored to have pipes to send water to their homes.
-A lack of clean water supply means that the water that is available is unsafe for drinking.
-the people are more prone to water-brone diseases which will lead to a poor standard of living and poor quality of life.

(vi) proper sanitation facilities
-Sanitation facilities includes proper flushing and proper waste disposal system.
-with proper sanitation facilities, it will allow the people to dispose their waste hygenically.
-with poor sanitation facilities, people will bury their waste in the soil or in the ground.
-this would contaminate the environment and water sources which would poss as a health risk
-it would in turn, lead to a poor standard of living and poor quality of life.

Education Indicators:
(vii) Literacy rate
-literacy rate refers to percentage of adults who are able to read and write in a country.
-with a higher literacy rate means that a large percentage of the population is able to read and write. this would mean that a larger percentage of the population would be employed in the secondary and tertiary industry { high paying jobs }. with more people in high paying jobs, the greater income per capita. a large proportion of the country can afford better goods and services which leads to a better standard of living and better quality of life.

Limitations of HDI and its indicators:
Like everything, there are limitations to these indicators as well as the HDI. for example, the economic indicators. when calculating the GDP per capita, we do not take into account income inequality. GDP per capita refers to the average income a person earns in a country. however, not everyone is working in the same industry or working in high paying jobs. for example:the GDP per capita of the USA has increased from 2002 to 2006 but the average wage in the USA remains flat because only 1% of the population benefit from the strong economic growth. the remaining 99% do not benefit much from the economic growth.

Another limitation is HDI is not accurate for LDCs. HDI do not take into account informal trading also known as barter trade. in informal trading, we exchange one good for another. no money is required in informal trading.

Two more parts. jiayous ! (: