Ordnance Survey – Great Britain's national mapping agency
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GPS (Global Positioning System) is a satellite-based positioning and navigation system owned and operated by US DoD (Department of Defense). Access is free for all users and the service is available 24 hours a day, 365 days a year. GPS is an all weather system that works anywhere in the world. GPS can give an instantaneous, real-time position to within approximately 10m using a single handheld receiver.