The telephone will work in a car, which has only a thin metal roof, but it might not beside a mountain or in an urban canyon in Manhattan.

ECONOMIST: Staying in touch | The

It doesn't even need to know what kind of signal it's looking at, and it can get its position in places there's no GPS to work from, whether it's in an urban canyon or the natural kind.

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In-car GPS developers have long had to wrestle with the urban canyon effect that blocks or bounces signals downtown: they often have to make best guesses for accuracy when they can't count on cellular or WiFi triangulation to pick up the slack, like a smartphone would.

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"A researcher I was speaking to recently reckons green walls in urban canyon environments (areas where walls are higher than the width of the road separating them) are more effective than trees at collecting particles because the way the wind eddies around and then moves down the wall, " Laurence said.

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And like many a fellow environmentalist, she is concerned that urban sprawl is now encroaching on surrounding conservation areas like Lake Mead, Spring Mountain and Red Rock Canyon.

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