In China, infrastructure and agglomeration affect how well cities work. This study looked at data from different regions in China. They found that having more non-farming jobs in city areas can make cities more productive but only up to a certain point. After that point, it helps a lot. This threshold isn't as high if you don't think about infrastructure. Infrastructure helps cities form groups that boost the economy. Big cities benefit more from these groups. So, infrastructure and having lots of non-farming jobs can really amp up how well a city works.