Contagious diffusion spreads by contact and skips nothing

Spread by contact, one neighbour at a time

Contagious diffusion is the spread of an idea, practice or disease through direct contact, so it moves from each carrier to the people and places nearest to them. The literature on cultural diffusion describes it as spread from person to person within a population without regard for hierarchies. The course framework lists it in Topic 3.4 as one of the three kinds of expansion diffusion, so the hearth keeps the trait while the area around it grows continuously.

What the map looks like

A contagious pattern widens like ink dropped on paper. Each new ring touches the last, adopters are densest near the hearth, and no island of adoption appears far away with untouched ground around it. That shape is distance decay at work: contact is easiest with near neighbours, so the spread slows as it moves outward. When a question shows a map with a solid, expanding patch rather than scattered dots, contagious diffusion is the first candidate to test.

Examples that score marks

Disease gives the type its name, and the textbook case describes an epidemic moving through a town household by household. Cultural traits behave the same way: a dance, a joke or a style of dress passes between friends, then between neighbouring schools, then across a city. The Swedish geographer Torsten Hägerstrand wrote his doctoral research on cultural diffusion, and spread between neighbours sat at the centre of that work. Online sharing is sometimes called contagious because it passes person to person without regard for rank, although its neighbours live in a network rather than on a map.

Contagious or hierarchical: the question that decides

Ask whether any nearer place was passed over. Hierarchical diffusion skips smaller or lower ranked places and lands in large or powerful ones first, leaving gaps. Contagious diffusion skips nothing. Real spreads often combine the two: the cultural diffusion literature notes that HIV and AIDS first spread to urban neighbourhoods hierarchically and then outward contagiously. If the question describes a jump between cities followed by local spread, name both types and put them in order.

The slip that costs the point

A quick spread tempts students to answer contagious. What decides the type is whether the spread moved through contact and left no gaps. A trend that appears in several major cities within days and reaches small towns months later is fast but hierarchical. A practice that creeps outward from one village over decades is slow but contagious. Judge the pattern by what it touched and in what order, and the speed will not mislead you.

Practising the diffusion types together

Revise contagious diffusion beside relocation and stimulus diffusion rather than on its own, starting from the diffusion diagram in your textbook. Photo to quiz turns that diagram into questions built around maps of spread, and the multiple choice test maker puts the same choice in the exam's format. The Unit 3 page covers the surrounding cultural patterns.

Last updated: 2026-09-27 · Written with AI assistance and reviewed before publishing.