Commons:Geocoding

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On Wikimedia Commons, geocoding is the practice of attaching geographic location information to media. When we geocode media on commons we identify the latitude and longitude from where the media was recorded and attach it to the description page using a {{Location}} or {{Location dec}} template. For jpeg images, geodata can also be stored in the image exif.

Geocoded images on a worldmap
As of February 2014, 4.4M Wikimedia Commons images are geolocated.

Media that is geocoded can be found in Category:Media with locations.

You can find coordinates for untagged pictures in: Category:Location possible. If you see an image that needs geotags, you can add {{Location possible}}.

Geocoding media on Commons[edit]

Geocoding is easy and only takes a couple of steps.

On Commons we record the location of the camera as accurately as we can. The locations of subjects should be geocoded on their Wikipedia articles, and the Commons description should link to those Wikipedia articles. Pictures can be geocoded in the camera, or in your own computer, or after uploading.

Automatic procedures[edit]

GPS or other automated methods can be especially useful in rural locations without landmarks which can be easily recognized in the aerial images. If your camera has a built-in GPS receiver (as most smartphone camera phones do) then your work is already done. Since November 2011, the Upload Wizard adds the proper Geocoding Templates from the GPS data stored in your images. For pictures not uploaded through the Wizard, {{GPS EXIF}} can be added to summon a bot to code them.

You can also use a separate GPS receiver to record the location while you are recording the media, and use computer software to merge the locations into the image files. Such software uses the camera time tag in the image file to look up the coordinates from the GPS. For accurate results, the camera time must be correct or the time error entered manually. The time error can be monitored by photographing the time displayed by the GPS. Errors caused by spotty GPS coverage can be adjusted by the same tools that are used for manual geocoding, though more easily since you already have an approximate position.

Adding Geotags before uploading[edit]

Some software, such as Microsoft Pro Photo Tools or Picasa *, allow you to add geographical information to images from a map. The upload wizard will also recognize these tags. You cannot add camera directions by this procedure, but programs such as Geosetter can insert metadata including : geographic coordinates of the location shooting, camera direction, and the name of the exact location.

If your camera has accidentally tagged your images with completely wrong geodata, you can remove them on a batch of pictures by using ExifToolGUI. It uses ExifTool that is also installed by Geosetter mentioned above.

* Picasa web albums also allow addition of geographical information from a map. But this information does not appear to be embeded in the image files and cannot be pulled back to ones own computer.

Manual procedures[edit]

The easiest way to identify the location in urban areas is to use an online mapping site with aerial imaging such as:

GeoLocator tool[edit]

Steps to obtain coordinates and build appropriate location tag:

  1. find your location on embedded map (move/zoom/search it as needed)
  2. place location marker on most exact location ([Alt+click] over your location, or by dragging a marker)
  3. define heading (camera view direction) from that location ([Shift+mouse move]/[Shift+click])
  4. copy resulting {{location}} or {{location dec}} markup

Steps to update an existing location tag (to improve location or to add heading):

  1. paste existing location tag into query box and press Apply. Tag gets parsed and location will appear on a map.
  2. update location marker to more exact location (by dragging it or by [Alt+click] over new location)
  3. define heading (camera view direction) from that location ([Shift+mouse move]/[Shift+click])
  4. copy resulting {{location}} or {{location dec}} markup back

Google Maps[edit]

  1. Open a new browser tab/window and load http://maps.google.com/.
  2. Search for the correct location (zoom in, Satellite mode is suggested).
  3. Right-click on the exact location the media was recorded and select Center map here
  4. Click the link icon in the left sidebar
  5. Copy the link in the top box (do not click short url)
  6. Use the Coordinate conversion helper to insert the coordinates on the image page (add a heading such as "N","SE","NNW")
    Check the page for instructions on installing and using it.

Google Earth[edit]

  • If you have Google Earth, a tool for geotagging can be installed: Ald-Hjl-Koord-en.kmz. A crosshair will appear in the middle of the Google Earth screen. Place the crosshair exactly over the camera location by moving the view, and click on it. The location template can be copied from the window that opens. (Please deactivate the tool if unused.)
  • If you have coordinates in a KML file (such as created in Google Earth and exported with "Save As" or "Copy", or aided by Picasa), the kmlconvert tool can be used to convert the coordinates to Commons templates. This method is suitable for geocoding a series of images.

See en:Wikipedia:Obtaining geographic coordinates for more information.

Precision[edit]

The linear measurement of a longitudinal angle varies according to latitude. If we are aiming to a precision of about 7 m, then it is appropriate to use decimal degrees with 4 decimal places. This is suitable in most cases. For the minute/second format, seconds with 1 decimal place will similarly give precision of about 1.5-3 meters of real earth surface.

Length Equivalent of Longitudinal Degree at Selected Latitudes in km
Latitude Town Degree ° Minute ′ Second ″ Decimal Degree at 4 dp
60 Saint Petersburg 55.65 km 0.927 km 15.42 m 5.56 m
51° 28′ 38″ N Greenwich 69.29 km 1.155 km 19.24 m 6.93 m
45 Bordeaux 78.7 km 1.31 km 21.86 m 7.87 m
30 New Orleans 96.39 km 1.61 km 26.77 m 9.63 m
0 Quito 111.3 km 1.855 km 30.92 m 11.13 m

Note that latitudinal degrees do not vary significantly across the Earth, having a surface precision of 1" = 31 m or 0.0001° = 11 m. See en:Geographic coordinate system for more information.

Geodetic system[edit]

All coordinates should be referenced to the en:WGS84 datum, the one supported by GPS systems and Google Maps. References taken from printed maps are unlikely to use this datum, and lead to inaccuracies in the order of hundreds of metres. National Grid reference systems use a local datum so will provide the wrong result.

Adding a location template[edit]

The use of the following templates is encouraged:

  • {{Location}} for degree, minute, second coordinates
  • {{Location dec}} for decimal degree coordinates
    • Example for southern hemisphere, decimal: location dec|-7.58|-14.24

Do not simply invent your own new templates or copy geocoding templates from other wikis without discussion. Doing so can break the automation that reads and uses the geocoding. Commons geocoding needs are also not the same as those of other projects. Note that you also should not create your own wrappers around {{Location}} or {{Location dec}}; this will break the automation as well. Just call one of the templates directly from the image description page.

Simply add {{location dec|lat|long}} to the image page, filling in the lat and long from the procedure above. If the image page has an {{Information}} template, or similar, the {{location dec}} template should come immediately after it. The result will look something like this:

Camera location 37° 30′ 40.9″ N, 77° 36′ 09.41″ W View this and other nearby images on: OpenStreetMap - Google Maps - Google Earth info

Alternatively, add {{location|lat deg|lat min|lat sec|NS|long deg|long min|long sec|EW}} to the image page, filling in the lat and long. If the image page has an {{Information}} template, or similar, the {{location}} template should come immediately after it. The result will look something like this:

Camera location 37° 30′ 40.9″ N, 77° 36′ 09.41″ W View this and other nearby images on: OpenStreetMap - Google Maps - Google Earth info
Compass points

Parameters[edit]

Wikipedia geocoding often uses parameters after the coordinates to give more information about the location, but some of them are not useful here.

  • type and scale - Redundant on Commons, as most images are at lowest scale. The defaults are type:landmark and scale:5000. These parameters should be given only if values different from the defaults are desired.
  • heading - Used to indicate the direction the camera was pointing at. It is given as degree values 0-360 (clockwise with north as 0) or a compass point abbreviation as defined in w:Boxing the compass. (Example: heading:NW)

Heading parameter related tools[edit]

  • Compass overlay can be displayed on Google Maps or in Google Earth to help find the correct heading:
    • Google Maps: map with fullscreen compass overlay
    • Google Earth: Compass_overlay.kml can be added to "My Places" and displayed when necessary. The overlay does not change when the view is rotated, so remember to click on the top right compass to reset the viewpoint orientation.
  • Google Earth 5.0 shows the heading in degrees with the "Ruler" tool, when a line is drawn from the camera location to the object in the center of the photo. The heading does not depend on viewpoint orientation.
  • GeoLocator tool allows interactive picking of correct heading on a map as part of metadata authoring.

Use of the information[edit]

Clicking on the coordinates on an Image page will lead to a list of various services that can show the location. It is also possible to browse Commons images on a map:

  • A world map with thumbnails of geocoded images can be found from WikiMiniAtlas on Commons.
  • Some Geocoded images from Commons plotted in Google Earth with GeoCommons (images tagged with {{object location}} are not displayed).
  • Some geocoded images from Commons plotted in Google Maps (images tagged with {{object location}} are not displayed).
  • In the "gadget" tab of Special:Preferences, there is an option "View category on Google maps". If enabled, this adds a link "map" to all categories. This shows the location of geocoded images in the category on Google maps.
  • Adding {{GeoGroupTemplate}} to a category page adds links to view the images in the category with various maps.

Things to do[edit]

  • Add geocoding to any location related media on Commons. Areas you know personally are easiest, but geocoding images from other areas based on satellite data and other photos is also possible. For help in finding material to work on, choose an interesting category and enter the name in this tool to see a gallery of images that need to be geocoded.
  • Find coordinates for untaged pictures tagged with {{location possible}} in: Category:Location possible.
  • Refine inaccurate geocoding on images that are off the correct camera location, or have been positioned in the exact same place as a number of other images (see list)
  • Monitor and fix tags of images with incorrect geocoding in Category:Media with erroneous locations and recently geocoded images (gallery).
  • Find coordinates with unknown headings and try to fix them (see list).
  • Verify or fix coordinates of images imported from external sources where geocoding may be less conscientious (see for example Flickr images)
  • Replace most usages of {{coor d}}, {{coor dm}} and {{coor dms}} with {{Location}} or {{Location dec}} in "File:" namespace pages.

Special:Preferences[edit]

Some of the tools can be activate in the "gadget" tab of Special:Preferences:

  • Locate images on Google Maps: On Category pages, adds a "Map" link to locate geocoded images from that category on Google Maps. [talk] 
  • Geocoding tools: Adds three geocoding links to the toolbox: recent changes, daily error log, and search [talk] 
  • Geocoding To Do: Add a tab to the category linking to the tool allowing to view images that are not geocoded. [talk] 

Participants[edit]

Geocoded images on Commons

See also[edit]