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The basic method of symbolizing rivers-apparent even on ancient maps-is that of showing thin tapered lines joining successively wider lines before eventually emptying into oceans (Figure 1). Wind roses appeared on maps as early as the 13 th century, but even before this the earliest illustrations that might arguably qualify as flow maps are those depicting rivers and streams. While the symbolic use of an arrow is thought to be less than four hundred years old (Finkel 2015), cartographers have long been interested in representing movement on maps, especially for maritime purposes. Topology: the non-metric spatial relationship (e.g., connected) between nodes Space-time path: a multidimensional graphic (often cubic) showing the path of an object – usually a person – through space over time also referred to as “time-space” path Sankey diagram: a type of non-cartographic flow diagram that depicts the volume of flow through a system with proportionally-sized arrows Radial flow map: a single source distributive flow map with flow radiating out from the origin Origin-destination (O-D) matrix: a matrix of origins and destinations indicating the volume of flow between each O-D pair Node: an origin or destination in a flow map or graph
Princeton university origin graphing series#
Network flow map: the classic flow map type showing a series of locations joined by lines representing paths of travel (often straight lines) of varying thicknesses indicating the volume of flow on each segment of the network Graph: a configuration of nodes and edges, as in a network graph Whatever their form, good flow maps should effectively visualize the relative magnitude and direction of movement or potential movement between a one or more origins and destinations.Ĭontinuous flow map: a type of map that depicts the movement of phenomena on a continuous surface, where the flow can be measured at any point (e.g., wind) also called called “unit vector” flow mapsĭistributive flow map: a type of map that depicts phenomena being distributed between nodes (e.g., exports from a country) in a geographic network
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In the extreme, such maps lack a geographic coordinate space and are more diagrammatic, as in Sankey diagrams, alluvial diagrams, slope graphs, and circle migration plots. Flow maps frequently use distorted underlying geography to accommodate the placement of flow paths, which are often dramatically smoothed/abstracted into visually pleasing curves or simply straight lines. Aesthetic considerations for flow maps are numerous and their production is often done manually without significant automation. Most flow maps typically use line symbols of varying widths, lengths, shapes, colors, or speeds (in the case of animated flow maps) to show the quality, direction, and magnitude of movements. Maps of this type often depict the vector movement of entities (imports and exports, people, information) between geographic areas, but the general method also encompasses a range of graphics illustrating networks (e.g., transit and communications grids) and dynamic systems (e.g., wind and water currents). Flow mapping is a cartographic method of representing movement of phenomena.