Researchers including a scientist at Texas A&M University said the spread shows no signs of stopping.
Texas A&M geographer Burak Guneralp said urban areas are growing even faster than urban populations.
"This massive urbanization of land is happening worldwide, but India, China and Africa have experienced the highest rates of urban land expansion," said Guneralp, who worked with researchers from Yale, Stanford and Arizona State on a study published in the journal PloS ONE.
The United Nations predicts there will be an additional 1.47 billion people living in urban areas by 2030, Guneralp said.
"Our study covered the 30 years from 1970 to 2000, and we found that urban growth is occurring at the highest rates in developing countries," he said.
"However, it is North America that experienced the largest increase in total urban land."
There is an upside to the urbanization trend, Guneralp said, noting in cities people exchange ideas and experiences that spur innovation and create business opportunities.
"Because of all these interactions, cities are the most likely places to come up with the solutions to the emerging environmental and economic challenges that we face," he said.