Urbanization increases the consumer class as well employment. More people in cities will create more jobs. A bigger consumer class will obviously consume more resources and employment ensures people have money to spend. These two together increase consumer spending and hence drives the economy and state spending.
For example: An increase in Urban population will increase the need of infrastructure, food, healthcare facilities, etc. and thus will increase the need of human resource creating jobs. These people will earn and spend thus driving economy. These people will save also...thus giving money back to banks. Banks give this money to industry in form of loans.
So, this a whole cycle and everything is connected.