What primarily distinguishes contagious expansion diffusion from other types?

Contagious expansion diffusion is primarily distinguished by its feature of simultaneous adoption of an innovation by many individuals or places that are closely connected. This type of diffusion occurs when a cultural trait or innovation spreads rapidly and widely through direct contact and interaction within a population. For instance, a viral trend or a popular social media challenge can quickly be adopted by a large number of individuals in a specific area before it extends further.

In contrast, other types of diffusion, such as hierarchical diffusion, typically involve a more structured process where influential individuals or institutions first adopt the innovation, followed by the general population. Additionally, contagious diffusion does not necessarily require travel to adopt the idea, as it can spread through communication or social connections without geographical movement. Therefore, the simultaneous adoption characteristic of contagious expansion diffusion sets it apart from these other diffusion processes.