Distance decay: interaction falls as places move apart

Geographers call it distance decay, and on a graph it appears as a curve that drops steeply at first and then levels off.

The pattern in one sentence

Distance decay describes what happens to interaction as places move apart: the number of trips, calls, shipments or visits between them falls, and it usually falls fastest over the first stretch of distance. The course framework names distance decay in its list of spatial concepts alongside location, place, flows and time space compression. The cartographer Waldo Tobler compressed the idea into what is now called the first law of geography, the sentence quoted at the top of this page and the starting point for most spatial analysis.

Reading the curve the exam draws

Questions often show a graph with distance on the horizontal axis and interaction on the vertical one. The line starts high near the origin, drops steeply, then flattens into a long tail, because the first few kilometres cost the most relative to the benefit of a trip. A steep curve means distance matters a great deal, which is typical of cheap and frequent errands such as buying bread. A flat curve means people will travel far, which is typical of rare and specialised services such as a transplant surgeon or a university.

Friction of distance is the cause, decay the result

The two terms are linked but not interchangeable. Friction of distance is the cost that separation imposes in time, money and effort; distance decay is the fall in interaction that this cost produces. When transport or communication gets cheaper, friction falls and the decay curve flattens. Time space compression works this way: places do not move, but the effective distance between them shrinks.

Examples that earn the mark

Migration offers the classic case. Ernst Georg Ravenstein, writing in the 1880s, observed that the majority of migrants move a short distance, and long moves remain rarer than short ones. Retail offers another case: a supermarket draws most of its customers from nearby streets and very few from across the city. The gravity model formalises the pattern, predicting that interaction rises with the size of two places and falls with the distance between them. Commuting, dialect boundaries and friendship networks show the same slope.

Where students lose the point

A frequent error is to claim that distance decay has disappeared because of the internet. Interaction still declines with distance for most activities; what has changed is the rate. Video calls and online shopping flatten the curve without removing it, while physical goods, commuting and most migration still show a strong decline. An answer that says the curve has flattened, and explains why, earns more than one that says distance no longer matters.

Practising the graph and the terms

Photograph the distance decay graph from your textbook together with your notes on friction of distance, because questions pair them. Photo to quiz turns the graph into questions that describe a change in transport cost and ask what happens to the curve, and the ones you miss come back through spaced repetition. The Unit 1 page lists the other spatial concepts in the same topic.

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