Flow Mapping Analysis
Also known as: Flow Map, Origin-Destination Mapping, Movement Mapping, Flow Cartography
Flow mapping analysis visualizes movement between places — migrants, commuters, trade, traffic — by drawing the flows of an origin-destination matrix as lines on a map, with line width scaled to the volume moving along each link. It is the cartography of interaction: where choropleths show what is in a place, flow maps show what travels between places, and the central challenge is to reveal the dominant patterns of movement without the map dissolving into an unreadable tangle of crossing lines. The technique was put on a computational footing by Waldo Tobler's 1987 experiments in computer migration mapping, and modern methods add edge bundling, smoothing, and statistical filtering to manage visual complexity.
Key highlights
- Shows movement and interaction geographically, which choropleth and symbol maps cannot.
- Encodes flow volume directly through line width, making dominant routes immediately visible.
- Edge bundling and smoothing can render even dense origin-destination matrices legible.
- Statistical filtering against a gravity baseline highlights structurally significant, not merely large, flows.
Intuition
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How it works
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When to use it
Use flow mapping analysis whenever your data describe movement or interaction between located places and you want to show its geographic structure — migration between regions, commuting between home and work, trade between countries, traffic between zones, or transfers between accounts. It is the natural display for an origin-destination matrix when both the magnitude and the geography of flows matter. It works best for a manageable number of dominant links or after bundling and filtering reduce a dense matrix to its structure; it is less suitable when there are so many comparable flows that no design can declutter them, when direction or net versus gross flow is the real question (where specialized chord or net-flow displays may serve better), or when location is irrelevant and a non-spatial network diagram would communicate more clearly.
Strengths & limitations
- Shows movement and interaction geographically, which choropleth and symbol maps cannot.
- Encodes flow volume directly through line width, making dominant routes immediately visible.
- Edge bundling and smoothing can render even dense origin-destination matrices legible.
- Statistical filtering against a gravity baseline highlights structurally significant, not merely large, flows.
- Dense matrices produce crossing-line clutter that bundling can only partly resolve.
- Bundling and smoothing distort the true paths of flows in exchange for clarity.
- Representing direction and asymmetric two-way flows clearly is difficult on a static map.
- Long lines between distant places can dominate visually regardless of their actual importance.
Common pitfalls
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Applications
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Frequently asked
What is edge bundling and why is it used in flow maps?
Edge bundling groups flow lines that run in similar directions through similar areas into shared, curved bundles, much as separate roads merge into a single highway corridor. It is used because a flow map of a large origin-destination matrix quickly becomes an unreadable hairball of crossing lines, and bundling collapses that tangle into a handful of legible trunk streams. The trade-off is that the bundled path of any individual flow no longer follows its true straight-line route, so bundling buys clarity at the price of geometric precision.
How do I decide which flows are significant enough to map?
Large flows are not automatically significant, because big, nearby places naturally exchange a lot simply due to their size and proximity. A standard approach is to fit a baseline model — most often a gravity model that predicts flow from the sizes of the two places and the distance between them — and then examine the residual, the difference between the observed and expected volume. Flows that are far larger than expected are the structurally interesting ones, and mapping only those dominant or over-represented links turns a cluttered map into a focused one.
How is flow mapping related to the gravity model of migration?
They are complementary. The gravity model is a statistical model that predicts how much flow to expect between each pair of places from their sizes and separation, while flow mapping is the cartographic display of the actual observed flows. The two combine naturally: the gravity model supplies the expected baseline, and the flow map can then show either all flows or, more powerfully, only the residual flows that the gravity model fails to explain, revealing the movement patterns that are surprising rather than merely predictable.
Sources
- 1.Tobler, W. (1987). Experiments in migration mapping by computer. The American Cartographer, 14(2), 155–163.
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Cite this page
ScholarGate. (2026, June 22). Flow Mapping Analysis. ScholarGate. https://scholargate.app/human-geography/flow-mapping-analysis