A flow map is a type of thematic map that uses linear symbols to represent movement. It may thus be considered a hybrid of a map and a flow diagram. The movement being mapped may be that of anything, including people, highway traffic, trade goods, water, ideas, telecommunications data, etc. The wide variety of moving material, and the variety of geographic networks through they move, has led to many different design strategies. Some cartographers have expanded this term to any thematic map of a linear network, while others restrict its use to maps that specifically show movement of some kind.
Many flow maps use line width proportional to the amount of flow, making them similar to other maps that use proportional size, including cartograms (altering region area), and proportional point symbols.
The earliest known map to visually represent the volume of flow were two maps by engineer Henry Drury Harness, published in 1838 as part of a report on the potential for railroad construction in Ireland, showing the quantity of cargo traffic by road and canal. In subsequent years, others experimented with the technique in Europe, until it was mastered by Charles Joseph Minard.
During the 1850s and 1860s, Minard published forty-two flow maps on a wide variety of topics among his cartes figuratives. Among these is his 1869 map of the French invasion of Russia in 1812-1813, which has been called "the best statistical graphic ever drawn." Many of Minard's maps use design techniques that have yet to be improved upon, even in the age of computer graphics.
During the 1980s, Waldo Tobler conducted experiments to create flow maps by computer. Early computer-generated maps were not up to Minard standards, but Geographic information system (GIS) and graphics software has improved in the ability to design flow maps.
A wide variety of flow maps have been created since the 1830s, showing movement in many forms.
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A visual variable, in cartographic design, graphic design, and data visualization, is an aspect of a graphical object that can visually differentiate it from other objects, and can be controlled during the design process. The concept was first systematized by Jacques Bertin, a French cartographer and graphic designer, and published in his 1967 book, Sémiologie Graphique. Bertin identified a basic set of these variables and provided guidance for their usage; the concept and the set of variables has since been expanded, especially in cartography, where it has become a core principle of education and practice.
This paper presents a state-of-the-art review of two-phase flow and flow boiling across horizontal tube bundles. The review covers studies related to the dynamic aspects of two-phase flow on the shell side of staggered and in-line tube bundles for upward, ...
Experimental test results for flow boiling of pure ammonia inside horizontal tubes were obtained for a plain stainless steel tube. Tests were run at a nominal saturation temperature of 4°C, nine mass velocities from 20- 140 kg/m2s, vapor qualities from 1-9 ...
1999
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The transposition of atmospheric turbulence statistics from the time domain, as conventionally sampled in field experiments, is explained by the so-called ergodic hypothesis. In micrometeorology, this hypothesis assumes that the time average of a measured ...