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Does the strength of GPS weaken in rural areas? For example, based on how the satellites work, would the strength in the centre of Australia differ from a populated city in Europe?

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    GPRS ain't really related to GPS you know. Are you sure you want to ask about two totally diffrent technologies? – Jakub Kania Nov 19 '13 at 12:27
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    To clarify: Unlike mobile phones (GPRS) who normally use ground based towers, the GPS signal comes from satellites orbiting the earth. So long as you can see the sky above you, you should be able to receive the GPS signals. – Rob Lodge Nov 19 '13 at 16:56
  • Anecdotally, the hand-held Garmin unit I carried to the foot of Uluru in the outback worked really well all over Australia. However, I often had to balance it on the motor-coach windowsill to get it to see enough birds to lock while driving from place to place. Visibility of the sky is a big factor, and there is lots of sky available over most of oz. – RBerteig Nov 19 '13 at 19:44
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For GPS, the simple answer is no. The strength of the signal from a GPS satellite is determined more by atmospheric interference and tree/foliage (or other) cover.

In fact, in large cities with tall buildings it can be more difficult to get high accuracy readings than it would be in an open farm field in the middle of nowhere. Tall buildings can block, or worse reflect the GPS signals. Tree canopies will be an issue pretty much anywhere that you want to collect that has trees, regardless of population density.

  • So theoretically in a desert GPS would work at its best? – S-K' Nov 19 '13 at 12:45
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    In general, yes a large open area is the best environment for using GPS. There may be other factors, specific to a desert that I can't really speak to (large amounts of dust in the air, etc), but I would expect it to work better than in a large city will tall buildings. – Evil Genius Nov 19 '13 at 12:53
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    Even with all the factors and error, Desert will be better than a city. – neogeomat Nov 19 '13 at 14:05
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    An anecdotal observation - here in the wide open spaces of New Mexico, I've seen my GPS (Garmin Map76csx) able to receive 12 satellites with the signal strength of ALL satellites pegged at max. Never seen it come close to that anywhere else. – Llaves Nov 19 '13 at 19:12
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    Something that is missing here is differential or RTK GPS, which may only have coverage within a certain distance of base stations or areas with mobile data connections available, depending on the method used. Of course, you can do your own RTK anywhere in the world if you have a reference mark to set up your own base station on (I think you usually need another mark to check with two). – Alex Leith Dec 3 '13 at 1:21
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(1) There is actually one factor that might be influencing some GPS receivers. To properly interpret the GPS signal, a GPS receiver must have certain data on position of the satellites, called the Almanac. These data can be downloaded from the satellites themselves, but that takes quite a bit of time (IIRC 12.5 minutes). As long as the GPS receiver does not have the full data, it might not be able to function properly and making you wait for the initial position.

If a GPS receiver also has mobile connectivity (so-called AGPS), it might be able to download the same data over the GPRS connection, which is much faster. And data connections are more common in cities.

So, while technically the strength of the signal is not any weaker in rural areas, usability of (especially older) GPS receivers might be worse.

(2) Professional GPS receivers can also use systems called DGPS, which use local up-to-second data on weather conditions to improve location measurement for the GPS system. This is technically not a part of GPS signal itself, instead a separate system that helps in making measurements more precise.

The DGPS signal may be broadcasted from a ground-based radio station, and these tend to be around populated areas. It might also be streamed over the Internet, which means that a data-enabled GPS receiver could provide better location measurements while in range of mobile data (assuming the receiver is actually capable of DGPS) — and again, mobile data has better availability in more populated areas.

So here again, while technically the strength of the GPS signal is not any weaker in rural areas, additional data potentially sent by local radio stations or streamed over data connections (whose availability is better in cities) might improve measurements.

  • Are you sure in (2) that you are describing DGPS and not something else? DGPS is differentially corrected GPS. It does not directly use any weather information. – whuber Nov 19 '13 at 18:27
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    @whuber: Well, I just wanted to make the description easier to understand by using some simplification. DGPS measures the difference of known fixed position to the one estimated using the satellite signal, which gets distorted by “weather” (ionosphere and trophosphere) conditions among other things. – liori Nov 19 '13 at 19:04
  • this article seems to support the argument that GPS in populated areas will be more accurate than unpopulated areas. In 2018 Australia decided to invest $260M in infrastructure to improve GPS accuracy from 5m to 1m. The infrastructure has already been deployed in Europe, North America and Asia. Obviously, this is a significant investment which is only worthwhile in populated areas. mashable.com/2018/05/09/gps-australia-investment-accuracy – craq Jan 15 '19 at 2:17
  • @craq: technically it's again not GPS itself, it's an additional system on top of it. Receivers will need to specifically support it, in a similar way to AGPS, DGPS etc. I'll amend my answer to make it clearer. – liori Jan 15 '19 at 17:54
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You might also take into account the things that influence GPS accuracy:

  • visibility of satelites
  • signal strength
  • distribution of satelites/spreading on sky

Esp. the last point can result in bad accuracy in populated areas with skyscrapers and high buildings. So the receiver might see 3 satelites, but they are mostly in one line, which makes it very difficult to produce precise results. Indicators for that are HDOP/VDOP values. Another aspect might be bad signal/noise ratio as in cities the EM spectrum is in heavy use (not sure about GPS frequencies). Also take into account that a GPS receiver will need more time to fix (getting the satelite atlas and solve equations) due to reduced visibility in metropols.

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There are many factors to this but the short answer is like @EvilGenius said: Everything depends on surroundings. Well, almost everything. Due to the satellite orbit GPS has problems near the poles. So in flat, open region it will work better than in the city unless you're in Antarctica.

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    Minor note, the orbits are around the equator and 55 degrees (three sets at that inclination), and they are 20,000km or 12,000 miles up, so the poles (and anyplace else with a good view of the sky) have good coverage. – Ronald Pottol Nov 19 '13 at 19:55
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    Well yes, the satellites are visible but they are low over the horizon which means many of them fall within the elevation mask and increased dilusion of precision. nrem.iastate.edu/class/assets/nrem446_546/week3/… (p. 58) – Jakub Kania Nov 19 '13 at 23:22
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This also depends what type of GPS you are using. If you are using a VRS (virtual reference station) then yes being out in the country will be more difficult than if you are in the city (assuming your base stations are located in the city, where most of them are) and you are operating outside the zone serviced by the stations.

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