References: link to original article by Adena Schutzberg http://www.directionsmag.com/entry/ten-things-you-need-to-know-about-gps/258449

1. 10 things You need to
know
About GPS

2. Definition
The Global Positioning System (GPS) is a
space-based satellite navigation system that
provides location and time information in all
weather conditions, anywhere on or near the
earth where there is an unobstructed line of
sight to four or more GPS satellites.
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3. The Generic Term
The generic term for these systems is Global
Navigation Satellite System, GNSS. There is
such systems as Russian`s GLONASS, USA`s
GPS, European project Galileo, etc.
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4. How GNSS Works 3
The satellites orbit
around earth and
broadcast
information. That
information is
basically a time
stamp.

5. GNSS Receivers Receive
GNSS receivers do not
have two-way
communication with the
navigation satellites;
the satellites are
broadcast-only.
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6. GNSS is not Great at Elevation
Horizontal accuracy for
recreational/consumer devices and many cell
phones is about +/- 10 meters (within a
tennis court) while vertical accuracy can be
two or three times that, about +/- 20 or 30
meters. The cause of this relies to geometry.
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7. Assisted GPS
With multiple GNSSs
online, or coming online,
and a variety of non-GPS
locating technologies in
use (wi-fi, cell tower,
etc.), there’s an effort to
bring them together for
enhanced solutions.
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8. GPS Interference
Because GPS signals from satellites are very
weak radio signals, they are susceptible to
interference by natural and man-made
signals.
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9. Government Control of GPS
While the U.S. Department of Defense
developed and operates GPS, it serves a wide
range of civilian users. To date, the
Department of Defense has never “shut
off” GPS in any part of the world, for any
reason.
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10. Navigating by GNSS
The GNSS only provides information to a
receiver to determine its current location,
velocity and time. Any other information,
such as the direction of motion, a suggested
route to a destination, a map, is provided by
software algorithms and stored map data.
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11. The GPS is Wrong!
• Most of the time a GPS receiver is correct in determining its
position, within its tolerance. If a navigation system fails to
provide an accurate route, other things are more likely to be the
culprit, for example:
• poor algorithm
• out-of-date street network
• wrong destination address
• The U.S. government received so many complaints on this matter
it compiled an article to explain to users how to “fix” such errors.
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12. This is the end