Real interesting Article at Latimes.com on improvements to the current GPS system.

Scientists and engineers — including those at a sprawling satellite-making factory in El Segundo — are developing an $8-billion GPS upgrade that will make the system more reliable, more widespread and much more accurate.

The new system is designed to pinpoint someone's location within an arm's length, compared with a margin of error of 20 feet or more today.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock