NOTICE: help.openstreetmap.org is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum

If you extract the coordinates of a specific position in OSM and enter them in Google Maps, you can notice a slight difference in position (about 3 meters).

What causes this difference and what's the purpose behind it?

asked 10 Apr '16, 02:55

applemano's gravatar image

applemano
(suspended)
accept rate: 0%

edited 10 Apr '16, 11:25

aseerel4c26's gravatar image

aseerel4c26 ♦
32.6k18248554

If Google and the OSM contributor were both using GPS there could well be a 3 metre margin of error as this in inherent in civilian grade GPS. As a geocacher I am familiar with this distance and the American cachers' remarks about 10 feet which is the same thing.

With aerial or satellite photos the camera is rarely directly overhead in which case the transformation of the photo onto the ground will incorporate a level of "best guess". I would be distrustful of an aerial photo if buildings seem to be "leaning" at a steep angle.

(21 Jul '23, 19:07) and1969

-2

The main difference between these two services is that every edit you make to OSM is owned by you and the community, while every change you make to Google Maps… will be owned by Google. The OSM community is what makes the project so special.

permanent link

answered 19 May '20, 06:23

Smith%20Hennry's gravatar image

Smith Hennry
-201
accept rate: 0%

The question is not answerable in a reasonable fashion without knowing which region you are talking about, and a specific example would be even better.

Most of the time OSM and google data is derived from very different sources and therefore you would not expect total agreement in any case.

permanent link

answered 10 Apr '16, 12:24

SimonPoole's gravatar image

SimonPoole ♦
44.7k13326701
accept rate: 18%

edited 10 Apr '16, 12:29

In order to correct the distortions in an aerial photograph, you have to know the exact height of the camera above every part of the ground, which is difficult because the ground is not flat. Topographical information of the required accuracy is expensive to create and is seldom published freely. Consequently published imagery can be in error by a few metres. A single GPS trace can easily be in error by a similar amount, but the average of several GPS traces, preferably taken at different times, probably represents the most accurate information available to most OSM contributors in most locations.

permanent link

answered 10 Apr '16, 11:49

Madryn's gravatar image

Madryn
2.2k365181
accept rate: 13%

There could be many reasons but the most likely is that your point of reference in OSM has a slight offset that was not taken into account by the person who mapped the object, especially if she used Bing imagery to help place it. The absolute location of Bing imagery varies quite a bit depending on the part of the world you're in, the nearness of hills or significant slopes. Also, there's a definite limit to the accuracy of consumer level GPS devices, typically 3-5 meters. And that accuracy can be decreased by sloping terrain, nearby buildings, etc..

Of course, Google isn't perfect either. The imagery they use is affected by terrain, slope, etc., just as is Bing imagery.

Cheers, Dave

permanent link

answered 10 Apr '16, 03:10

AlaskaDave's gravatar image

AlaskaDave
5.4k76107164
accept rate: 16%

Here is an OSM article that describes imagery and offset/alignment: https://wiki.openstreetmap.org/wiki/Using_aerial_imagery

(19 Jul '23, 18:28) DanielDoherty

Follow this question

By Email:

Once you sign in you will be able to subscribe for any updates here

By RSS:

Answers

Answers and Comments

Markdown Basics

  • *italic* or _italic_
  • **bold** or __bold__
  • link:[text](http://url.com/ "title")
  • image?![alt text](/path/img.jpg "title")
  • numbered list: 1. Foo 2. Bar
  • to add a line break simply add two spaces to where you would like the new line to be.
  • basic HTML tags are also supported

Question tags:

×29
×20
×19
×5

question asked: 10 Apr '16, 02:55

question was seen: 8,531 times

last updated: 21 Jul '23, 19:07

NOTICE: help.openstreetmap.org is no longer in use from 1st March 2024. Please use the OpenStreetMap Community Forum