The rapid growth of cities worldwide over the next two decades will cause significant risks to people and the global environment, according to analysis. Researches from Yale and Stanford predict that by 2030 urban areas will expand by 590,000 square miles--nearly the size of Mongolia--to meet the needs of 1.47 billion more people living in urban areas. "It is likely that these cities are going to be developed in places that are the most biologically diverse," said Karen Seto, a famous scientist at Yale University. "They are going to be growing and expanding into forests, biological hotspots, savannas , coastlines--sensitive and _ places." Urban areas, they found, have been expanding more rapidly along coasts. "Of all the places for cities to grow, coasts are the most sensitive. People and buildings along the coast are at risk of flooding and other environmental disasters," said Seto. The study provides the first estimate of how fast urban areas globally are growing and how fast they may grow in the future. "We know a lot about global patterns of urban population growth, but we know significantly less about how urban areas are changing," she said. "Changes in land cover associated with urbanization lead to many environmental changes, from habitats loss and agricultural land conversion  to changes in local and regional climate." The researchers examined studies that used satellite data to map urban growth and found that from 1970 to 2000 the world's urban footprint had grown by at least 22,400 square miles--half the size of Ohio. "This number is numerous, but, in actuality, urban land expansion has been far greater than what our analysis shows because we only looked at the published studies that used satellite data," said Seto. "We found that 48 of the most populated urban areas have been studied using satellite data, with findings in journals. This means that we're not tracking the physical expansion of more than half of the world's largest cities." Half of urban land expansion in China is driven by a rising middle class, whereas the size of cities in India and Africa is driven primarily by population growth. "Rising incomes translate into rising demand for bigger homes and more land for urban development, which has a great effect on biodiversity conservations, loss of carbon sinks and energy use." According to the passage, the most dangerous place for city expansion is the   _  .
forest desert savannas coastline