Point Map

Can a Smartphone Replace a Dedicated GPS?

How accurate can a smartphone GPS be?

Is a smartphone now good enough to replace a dedicated GPS receiver in the field?

These two questions have come up numerous times this past semester. Saratoga Springs is in the process of working on a tree survey and the GIS Center has been doing some minor supporting work. Since most people don’t own a dedicated GPS unit, tree surveyors were curious to know if a smartphone would be sufficient. This piqued our interest, as it could make our work easier if students could use their phones in the North Woods or around campus to collect location data.
To answer this we conducted a simple experiment. To begin, we used two Garmin GPSmap60CSx, a Verizon iPhone4S, and an AT&T iPhone 4S. Walking around a loop on campus, we recorded waypoints at known locations that were visible in satellite imagery and aerial photos. We loaded these waypoints into Arc Map, registered the actual locations, and then measured the relative error of the GPS units and the iPhones. Here are the waypoints, overlaid on the imagery layer of campus. The canonical location is in blue, the GPS units are in red, and the iPhones are in green.

The short analysis is that iPhones are still worse than a dedicated GPS, but not that much worse. For general positions, an iPhone is perfectly sufficient if you are fine with single-digit meter errors. If you want to be within a meter or two, a GPS is the best bet

The following table contains the distance from the canonical location to the GPS units and the iPhones.

  Site #     iPhone 4S (AT&T)     iPhone 4S (Verizon)     GPS Unit 1     GPS Unit 2  
    1     18.28     14.07     0.24     2.50
    2     6.06     5.80     0.83     0.81
    3     6.22     9.72     2.71     3.17
    4     2.74     5.43     3.05     3.31
    5     6.11     5.19     2.45     0.75
    6     6.44     8.78     4.43     2.84
    7     10.75     5.19     3.15     1.00
    8     13.88     8.40     2.06     0.84
    9     10.64     13.28     3.31     3.51
Avg. w/out 1       7.86     8.43     2.88     1.69

To get an average that represented the majority of the sample, we removed the first point from the table. This data point was collected right after moving outside from indoors, and my best guess is that the location information that the iPhones received was from WiFi triangulation and did not have information from more reliable sources(cell towers and GPS signals). Removing the outlier resulted in an average that better represented the other eight results.
I believe that we have reached a point where smartphone location is good enough for projects that are “campus-sized”. When points are separated by large distances, the position provided by iPhones is accurate enough to discriminate between locations. If precision is paramount or points are close together a GPS unit is still required to get significant results.

24 Comments on “Can a Smartphone Replace a Dedicated GPS?

  1. This is great info. What app were you using? Developers have some options for location accuracy settings — they can make them less specific (usually for privacy reasons).

    It would be interesting to compare accuracy depending on time spent at location with a phone, and number of location points stacked on the handheld GPS.

    A key here was whether you were still within cell phone, 3G, and wifi range. My experience is that once you stray from cell coverage areas and rely soley on the iphone GPS, my location accuracy has varied more — even by more than a mile.

    • Thanks for your comment! We used Trails (Developer, iTunes) on both iPhones. We were definitely still in 2G & 3G coverage areas for the entire test. We plan on doing some further experiments in slightly more remote locations, so we should have some more information in the future.

  2. When you combine the “good enough” location from a smartphone with a location tagged photo there’s not much doubt about what you have “located”. Many cities now provide phone apps that let citizens post work requests with a location and photo directly to the cities’ asset management systems. Cities love it because it reduces call center traffic and the city knows what to expect before they arrive on site and can therefore deploy the appropriate assets.

  3. Pingback: Why Hasn’t the iPhone Killed the GPS Unit? |

  4. Pingback: Why Hasn't the iPhone Killed the GPS Unit? | | info.mygarmin.biz

  5. Not if your in the deep woods. There are places where there is no reception from cell towers which are how the cell phones get their GPS coordinates. A dedicated GPS using the 24 satellites will save your ass if you are out in the boonies, e.g. the Flat Top Range in Colorado.

  6. Avenza Systems PDF Maps app for iOS (free) enables users to plot points on any georeferenced base map, add attribute data to the points (including photos), export/share data, import KML point data, and measure distances and areas. Everything can be done in the deep woods (except import/export) since the iPhone/iPad does not need cell or wifi reception to locate the GPS signal.

  7. For casual users, sure go ahead and use your Iphone or Android gps applications.

    For hikers, deep woods cover, don’t even think about it. Buy a dedicated gps unit. The reception, let alone battery life and useability (planning routes, export/import data), of a handheld gps unit exceeds that of our lovely little toy phones.

  8. The GPS reception on the iPhone/iPad is as accurate on a hike in an unpopulated area as it is in suburbia. You do not need a wireless or cellphone connection, although if you do have a connection your device may access the GPS signal sooner. That’s the only difference – the wireless or celltower connection will enable your device to determine your location a bit faster than it can without it. As the study above demonstrates, the positional accuracy of the iPhone is not far from a dedicated GPS receiver. I wouldn’t spend the extra money on a dedicated GPS device if I had my iPhone with me.

  9. Thanks for the valuable information!
    I am looking for an academic publication examining accuracy of smartphones assisted-GPS in comparison to GPS devices. are you familiar with any?
    Cheers, Orit.

  10. Hmh, comparing true gps device ( garmin) with assisted gps device ( iphone) is not very usefull.
    Iphone relies on mobile signal. In areas without it ( like real wilderness) it’s worth nothing.

  11. Awesome article! But I think that an iPhone gps will never be able to compete with a full Garmin/Tom Tom dashboard gps. Especially with Apple’s new terrible maps…

  12. Try that same test in the real world under trees, in canyons, or between high rise buildings and the relatively weak GPS receiver on the cell phone won’t see the satellites where as a dedicated GPS will continue to work just fine.

  13. Smartphones DO NOT rely on a mobile signal to function. As previously brought up a Smartphone willl probably acquire a position faster using data collected while within cell coverage but it is not a requirement.

  14. I came here wondering of the posibilities of the iPhone compared to a Garmin. One person says “As Good” another person says “not as good or useless”. now I wonder Why i even came here. You’re all confused, now so am I. To h$@% with you all.

  15. We’re almost one year later, would smartphone accuracy have improved with the iPhone 5 (or Samsung S3 etc.)? Any other interesting links available on the subject? Thanks.

  16. I understand the reason for removing the results of waypoint #1. However, since only the phones were off significantly, I would conclude that not only is a dedicated GPS more accurate, but it picks up and processes signals more quickly once turned on.

  17. Cellphones both smartphones and feature phones can return position accuracy levels comparable to gps trackers depending on the carriers internal settings. Sprint for example enables AGPS data on all phone connected to their network and without an app or software on the phone it is possible to get consistent location data accurate to within 30 feet.

  18. My tests using the iPhone5 and the same Garmin 60CSX have found and inverse result, and I used US Geodetic Survey Marks for my tests!

    Most of my tests were in good cell phone range, but a few were NOT. Only change was that it took longer for the phone to settle.

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