When things agglomerate, they gather together into a cluster or a group. In some states, people tend to agglomerate into cities, leaving rural areas sparsely populated.
You might come across the verb agglomerate in business news — moguls tend to agglomerate companies, collecting them under one controlling interest. You could also describe a website that agglomerates news items, gathering them all into one place. The Latin root word is agglomerare, "to wind or add onto a ball," from ad, "to," and glomerare, "ball of yarn."