In the next 40 years, the world’s population will increase by approximately two billion people. That means a global population of 9 billion by 2050. Because most of the growth will take place in the cities of the world’s developing countries, it won’t affect Americans—will it?

It certainly will, says John Weeks, demographer and professor of geography at San Diego State University.

“Virtually every social, political and economic problem facing the world has demographic change as a root cause,” said Weeks. “What happens in developing countries is not isolated; it will have an impact on our lives. And if economies in these countries improve, so will the political and economic stability of the region—something that will benefit the rest of the world.”

Little is known about the population of many developing nations or how to help their communities grow without sinking deeper into poverty. But research by Weeks and others has shown that good health is one crucial element of an economically productive population.

“If you are not very healthy, you’re simply not going to be very economically productive,” Weeks explained. “We are trying to determine how to help people in these developing countries achieve a higher level of health, and in the process, a higher level of productivity that will lift them out of poverty.”

Using GIS technology, Weeks’ research examines health and fertility measures of developing cities from a spatial analysis perspective. His team’s current work in the city of Accra, Ghana, uses satellite imagery, survey data and census data to identify the locations of good- and poor-health communities and then engages the people on the ground to confirm the findings.

Weeks’ earlier work in Cairo, Egypt, uncovered an interesting correlation between two seemingly unrelated factors—the abundance of vegetation and the fertility levels in a particular neighborhood. He and his colleagues found that in areas with more vegetation, socio-economic levels were generally higher and fertility rates lower.

The Cairo study, funded by the Andrew Mellon Foundation and the National Science Foundation, led to two successive awards from the National Institutes of Health to test Weeks’ theory in Accra. His discovery of the connection between vegetation and fertility levels will help governments and international aid groups target health intervention programs for citizens of the region.

A proposal is already in the works to extend his field research to other sub-Saharan African cities, where future population growth is projected to be the highest of all continents.

This plays into Weeks’ long-held belief that everything in the world is interconnected. At a young age, he resolved to figure out exactly how this interconnectedness played out. No easy task.

But he found an advocate in world-renowned sociologist and demographer Kingsley Davis, a mentor during Weeks’ undergraduate and graduate studies at the University of California, Berkeley. Davis told his students that the seemingly undecipherable questions don’t have to remain mysteries.

It’s a lesson Weeks tries to teach his students every day.

“If you don’t understand demographic change then you are not going to understand why the world is the way it is,” he said. “Understanding the connections leads to a better knowledge of the world, and that helps you negotiate it.”

John Weeks is San Diego State’s 2011 Albert W. Johnson Lecturer. He will speak about his work at 3 p.m. on March 11 in the College of Arts and Letters, room 201. Admission is free. His new book, “Irresistible Forces: Latin American Migration to the United States and its Effects on the South,” is co-authored with his son Gregory, a political science professor at the University of North Carolina, Charlotte.