Definition
DOP expresses how satellite geometry amplifies ranging errors into position errors: position error approximately equals the user equivalent range error multiplied by the relevant DOP. Widely spread satellites give a low figure, while satellites clustered in one part of the sky give a high one. Horizontal DOP below about 2 indicates good geometry for navigation, values above roughly 5 warrant caution, and the NMEA GGA and GSA sentences report it directly.
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