digital edition


Ebb and Flow

By Anna Fixsen
April 01, 2014
Map © Nelson Minar

As a deluge poured down in Grass Valley, California, in late 2012, software engineer Nelson Minar took to a cerebral rainy-day activity: tinkering with datasets and open-source software. He had recently learned of the National Hydrography Dataset—a collection of digital vectors compiled by the U.S. Geological Survey representing the drainage networks of rivers across the country—and the downpour outdoors inspired him to take a closer look at how the data could be used with mapping technologies.

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Over the next few months, Minar imported the National Hydrography data into PostGIS, a geographic database, wrote code to extract simplified versions of the rivers' shapes, and then drew them using JavaScript in a Web browser. "The challenge in making a map like this was the millions and millions of little lines in the data," Minar said. "I put a lot of time into paring it down." This arduous visual and technological exercise (memorialized by Minar in an online tutorial last May) resulted in an interactive Web map of the United States defined almost entirely by sinewy blue veins of water-flow networks. The richness of the data enables viewers to zoom in to get a hyper-local sense of an area's water systems. Minar, who has since relocated to San Francisco, compared his map to a modern-day version of those created by cartographer Harold Fisk, who was commissioned by the U.S. Army Corps of Engineers in the 1940s to chart the historic course of the Mississippi River.

Minar would be the first to caution viewers that the map doesn't necessarily indicate the location of rivers but rather identifies the elevations where water is likely to flow. The map is far from perfect, with certain areas lacking topographical information, but Minar is intrigued by the sculpting force of water—how, over millennia, rivers have etched the surface of the United States. "I was struck by its beauty," he said of the map. "We read about water systems being fractal, and beautiful—here you can really see that."


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