I'm working on a shapefile viewer for Android, and the file I'm using to test shows the surface land management for the state of Arizona. I zoomed all the way in on the north-west corner of the state and saw this. (The dotted gray line is Google's state line; the green line is mine.)

enter image description here

It looks like my math is off, or the shapefile is wrong, but then I zoomed in on the north-east corner of the state and saw this:

enter image description here

Google's state lines miss the Four Corners Monument by quite a bit, while mine are almost dead on. (I also checked in satellite mode; again, my state lines are almost perfectly on the Monument.) This led me to read the whole backstory of the Four Corners Monument being in the "wrong" place. But the final Supreme Court ruling was that the original survey markers are the legal border, not the description of where the borders were supposed to be.

Has Google drawn its state lines incorrectly? Perhaps they used the nominal borders instead of the survey markers?

  • 2
    Have you compared your and Google's data in other places as well? If the error is systematic, I would suspect a projection error rather than incorrect data. – karpfen Aug 31 '16 at 9:19
  • 1
    Also, even if not relevant in your case, Google does deliberately mess with borders occasionally, so be careful. See this article about disputed borders in Google Maps: thenextweb.com/shareables/2014/06/24/… – karpfen Aug 31 '16 at 9:23
  • How accurate do you want it to be? Every dataset should fit it's purpose. – FelixIP Aug 31 '16 at 9:29
  • @karpfen In my first screenshot, there's a shaded green area denoting some kind of park. Wherever that kind of shading runs along state or national border, the lines from the shape file tend to agree with the shading, while Google's border lines are a bit off. You can see the discrepancy on their web map here. The border from the shape file aligns perfectly with the green shading at that point. – Kevin Krumwiede Aug 31 '16 at 9:34
  • @FelixIP The dataset isn't the thing under test. I'm trying to determine whether my app is displaying the shape file correctly. Of course, if something is amiss I'll have to determine whether the file itself is accurate. But it looks like the political borders on the base map are very sloppy, because otherwise there's an error in the viewer and/or the file that is repeated almost exactly in some of the other features of the base map, which seems improbable. – Kevin Krumwiede Aug 31 '16 at 9:43

For this question to be answered reasonably, you need to define 'Reliable'. And secondly, considered Reliable by whom?

Strictly speaking, any Data, including maps is only valid as long as it is certified by some legal Authority. Anyway can create a dataset, and claim it is accurate and reliable, but unless it certified by a legal Authority, it has no legal validity.

Coming to the issue that you are seeing. The issue can be due to a variety of issues, such as transformation issues, digitization issues, or incorrect raw data. These issues can be in the resulting data, or in the source itself from which this data was created. These issue could be in your dataset, or in Google's Dataset.

Finally, Google does claim in its Terms and conditions, that it is not responsible for any issues that arises due to accuracy issues of its data.

Lastly, as an Added bonus, you should be aware that its boundary data was so wrong, that it sparked off a Military Skirmish.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.