NASA Satellite Images of Istanbul Put Causes and Consequences of Urban Sprawl in Stark Relief

Istanbul in 1975. Vegetated areas appear red while urbanized ones appear gray in this satellite image.

Recently released satellite photos of Istanbul provide striking visual evidence of what building more roads can do to a city -- and the results aren't very pretty.

A NASA Earth Observatory image acquired from a Landsat satellite in 1975, when Istanbul's population was around 2.5 million, shows a relatively small area of urban settlement (depicted in gray) surrounded by broad swathes of red (representing "plant-covered land").

More Roads Mean More Sprawl
Thirty-six years later, by which time the city's population had swelled to more than 13 million, many of those red areas had, unsurprisingly, turned gray. But the pattern of urbanization appears quite strongly to be not just the result of more people, but of more roads:

Istanbul in 2011. Development is clearly following the new roads (depicted as purple lines) leading to the second Bosphorus bridge.

In 1973, the first bridge across the Bosphorus opened, connecting the Asian side of Istanbul to the European side. The bridge is faintly visible in the 1975 image, and the urban areas in the newly connected east are near the bridge. In 1988, Istanbul opened a second bridge across the Bosphorus. Farther north, this bridge is visible in the 2011 image. Not surprisingly, the dark gray of dense settlement has filled in the area between the two bridges on both sides of the strait.

(NASA's website has a cool image comparison feature that overlays the 1975 and 2011 pictures to make the contrast even starker.)

No Solution To Traffic Problem
Opponents of a controversial plan to build a third bridge over the Bosphorus have long argued that it would have a similar effect as the first two spans, destroying green areas, increasing sprawl, and doing little to ease the city's traffic woes.

But while forward-thinking municipalities in the United States and elsewhere are recognizing that building more roads typically creates more traffic -- and even removing highways to reduce congestion -- the Turkish government is plowing ahead with its unpopular bridge plan. If they succeed in building the span, and the 400-plus kilometers of road that would go along with the project, it's not hard to imagine what a satellite image taken in 2047 would show.

NASA Satellite Images of Istanbul Put Causes and Consequences of Urban Sprawl in Stark Relief
Building new roads has been a major contributor to the city's unsustainable growth, newly released Landsat photos show, but more of the same appears to be on the horizon.

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