What is the relationship between unemployment and rapid population growth?

There is a direct correlation between unemployment and rapid population growth. For several reasons, both unemployment and population growth cause the other to increase.
First, unemployment tends to increase population growth. The main factor in this is a tendency for groups with lower education to have higher birth rates. Unemployment contributes to lower education because either people can't afford to send their children to college or the children end up dropping out early to earn money and provide for themselves and their families. This lack of education is directly related to increased birth rates and therefore to rapid population growth.
On the flip side, rapid population growth causes unemployment to rise because there are more and more people and not enough jobs to be filled by everyone. Additionally, an individual with a larger and/or rapidly growing family (5 children instead of 2 children, for instance) will have much greater expenses and a greater likelihood of bankruptcy, home foreclosure, or debt, which often begins a downward spiral.

Theoretically, rapid population growth should raise the unemployment rate because it would increase the number of people in a country without providing sufficient time for the creation of new jobs. However, rapid population growth through a sharp increase in the birth rate may not have much impact on unemployment or, in a country that isn't running at maximal employment, it may decrease unemployment. This is because a sharp increase in the birth rate would increase the number of infants. Parents would need to purchase more goods for these infants, thus driving up demand and potentially bringing unemployed people into various industries in order to increase the supply. As these infants grew up they would continue to force an increase in consumption without requiring job openings for them. However, when this cohort entered adulthood there would likely be some increase in the unemployment rate because there would still be more individuals that job openings.

Rapid population growth causes unemployment. Usually, firms hire people based on their skills and expertise; the management looks at the added value that the individual brings to the company. Furthermore, firms can only hire up to a certain limit because they have limited resources and limited needs. Rapid population growth happens when the number of people within a state or territory rises substantially over a short period of time. This scenario often leads to excess labor supply: there are more people looking for jobs than the firms are willing to hire. As a result, most of them are forced to fend for themselves. In developing countries, family planning measures are being encouraged as a way to control the population surge and minimize poverty levels because resources are too scarce to cater to the huge population.

In general, the relationship between unemployment and rapid population growth would be a positive/direct correlation. This means that as one increases, the other also increases. As a population rapidly grows, so does the number of unemployed people. This occurs because rapid population growth generally isn't met with growth of employment opportunities at an equal rate. As a population grows, more and more people are competing for the jobs that currently exist, and not everybody can be hired; therefore, more people are left unemployed.
It is possible that rapid population growth doesn't effect the unemployment rate; however, this only can occur if the number of jobs available increases as the population increases. More people in an area does mean that businesses have to scale up in order to meet the increased demand. That will create jobs, but if the influx of people is greater than the employment scaling, then unemployment will rise.