A study looked at where Chinese factories are located. They checked data from two industrial censuses in the 1980s and 1990s to see how manufacturing spread in China. They found that in 1995, many factories were bunched together in coastal areas. This meant that over time, factories were grouping more in certain regions. The researchers used math to figure out that this happened because it made it easier and cheaper for factories to operate close to each other. This is because when they're near other factories, they can get materials and sell goods more efficiently, saving money and working more effectively.