AP® Human Geography · Unit 3 · Topic 3.4
Hierarchical, Contagious, and Stimulus Diffusion
Hierarchical diffusion jumps between big places first, contagious diffusion spreads outward to every nearby person or place, and stimulus diffusion spreads only the underlying idea while the specific trait gets reinvented locally.
Expansion diffusion means a trait spreads while staying in its origin place and also taking root in new places, and it comes in three flavors that differ in who gets reached first. Hierarchical diffusion moves through a ranked order of places, usually by population or importance, so a new trend hits New York, Los Angeles, and Chicago before it ever reaches a small town two hours outside any of them. The trend skips over nearby small places because it is traveling through networks of influence, media, business, fashion, not through physical closeness. Contagious diffusion works the opposite way: it spreads outward from a source to everyone nearby regardless of rank, the way a cold spreads from one infected person to whoever they sit near, then to whoever those people sit near. Distance from the source predicts who catches it next.
Stimulus diffusion is stranger. The specific trait fails to transfer, but the idea behind it does, and someone in the new location builds their own version of it. A sandwich chain's actual sandwich might flop in a new country, but the concept, bread plus filling, survives and gets rebuilt with local flatbread and spices into something that succeeds. That is not the original item spreading; it is the concept spreading while the item gets reinvented, which is what separates stimulus diffusion from ordinary expansion diffusion.
These sit alongside relocation diffusion, where a trait moves because people physically migrate and carry it with them, leaving the origin behind. The internet complicates hierarchical diffusion especially: once information can reach anyone instantly, the climb down the urban hierarchy can collapse, letting trends appear in a small town and a megacity at nearly the same moment.
Key terms
- Expansion diffusion
- A trait spreads outward while remaining established in its place of origin.
- Hierarchical diffusion
- A trait spreads through a ranked order of places, such as largest cities first, rather than by distance.
- Contagious diffusion
- A trait spreads rapidly and widely to all nearby people or places regardless of status or rank.
- Stimulus diffusion
- The underlying idea of a trait spreads and gets reinvented locally, even though the specific item itself fails to transfer.
- Relocation diffusion
- A trait spreads because the people carrying it physically migrate to a new location.
Watch it explained
- How it worksHow does hierarchical diffusion jump down an urban hierarchy instead of spreading outward?
- How it worksWalk me through contagious diffusion spreading a disease outward from a single point.
- Worked exampleShow me hierarchical, contagious, relocation, and stimulus diffusion animated on the same map.
- Going furtherWhat happens to hierarchical diffusion once the internet removes the need for proximity?
- Common mistakeWhy isn't stimulus diffusion the same as copying the original idea?
Check yourself
End of topic.