metro是什么意思？

with the exception of South Africa, the only light rail metro system in sub-Saharan Africa is in Addis Ababa, Ethiopia.

So what factors, at the community level, do predict if poor children will move up the economic ladder as adults? What explains, for instance, why the Salt Lake City metro area is one of the 100 largest metropolitan areas most likely to lift the fortunes of the poor and the Atlanta metro area is one of the least likely?Harvard economist Raj Chetty has pointed to economic and racial segregation, community density, the size of a community's middle class, the quality of schools, community religiosity, and family structure, which he calls the single strongest correlate of upward mobility.