Commons:Geocoding

From Wikimedia Commons, the free media repository

Jump to: navigation, search


Shortcut: COM:GEO or COM:GC

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 template. For jpeg images, geodata can also be stored in the image exif.

Geocoded images on a worldmap

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

Contents

[edit] Geocoding media on commons

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.

[edit] Automatic procedures

If your camera has a built-in GPS receiver then your work is already done. User:DschwenBot goes through all new uploads every other day and adds the proper Geocoding Templates from the GPS data stored in your images.

[edit] Adding Geotags before uploading

Some software, such as a combination of Picasa and Google Earth, allow you to add geographical information to images. The bot will also recognize these tags. You cannot add camera direction by this procedure.

[edit] Fully manual procedure

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

[edit] GeoLocator tool

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

[edit] hjl_geocoding tool

Three steps to get coordinates:

  1. search your location within the map
  2. click the appropriate button
  3. copy text

Notes

  • Does not work well with Opera, after pressing the Button switch to User Mode to view and copy the coordinates. (Seems to work all right with the new Opera 9.5/Linux)
  • Site does not work well with Firefox/Mac.
  • The JavaScript in your browser must be enabled

[edit] WikiMapia

  • Go to WikiMapia.org
  • (Optional) Set View->Hybrid in the menu, so you can see the roads.
  • Place the crosshair over the desired location.
  • Locate the coordinates within the URL, e.g.: http://www.wikimapia.org/#lat=36.0368324&lon=-78.9001286&z=18&l=0&m=h&v=2
  • Copy-paste the coordinates into the appropriate template, e.g.: {{location d|36.0368324|-78.9001286}}

[edit] Google Maps

[edit] Method1

Place the cross hair exactly over the place and click on it. Then copy the template {{Location}} to Commons (Copy+Paste).

[edit] Method2

  • (Do only once) create a bookmark and enter the following for 'location':
    • javascript:void(prompt('',"{{location dec|" + gApplication.getMap().getCenter().lat() + "|" + gApplication.getMap().getCenter().lng() + "}}"));
  • Open a new browser tab/window and load http://maps.google.com/.
  • Search for the correct location.
  • Click on "Satellite" if it helps to find the location more easily, and zoom in.
  • Click on the exact location the media was recorded to center the map.
  • Click on your bookmark and you'll get a prompt with the geocode tag to add to the image.

[edit] Method3

  • Open a new browser tab/window and load http://maps.google.com/.
  • Search for the correct location.
  • Click "Satellite" and zoom it.
  • Click on the exact location the media was recorded to center the map.
  • Click "Link to this page"
  • Now, either:
    • Look in the url for a string like ll=37.51136,-77.602615. The numbers are latitude, longitude; you have identified the location.
    • Or, use the Coordinate conversion helper which assists you with the geocoding process. Check the page for instructions on installing and using it.

[edit] Google Earth

  • 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.

You can also use other means, such as a GPS receiver to determine the location while you are recording the media. This can be especially useful in rural locations without landmarks which can be easily recognized in the aerial images.

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

[edit] Precision

The linear measurement of an angle varies according to Latitude. If we are aiming to a precision of about 7m, then it is appropriate to use decimal degrees with 4 decimal places. This is suitable in most cases.

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

See en:Geographic coordinate system for more information.

[edit] Geodetic system

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.

[edit] Adding a location template

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 should also 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 top of the image page, filling in the lat and long from the procedure above.

The result will look something like this:

Camera location

37.51136° N, 77.602615° W

See this image at its location on Google Maps

This location on: Live Maps - MapQuest - Yahoo! Maps

or add {{location|lat deg|lat min|lat sec|NS|long deg|long min|long sec|EW}} to the top of the image page, filling in the lat and long the result will look something like this:

Camera location

37°30′40.9″N, 77°36′9.41″W

This and other geocoded Commons images: (Info)
Compass points

[edit] Parameters

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)

[edit] Heading parameter related tools

  • Compass overlay can be displayed on Google Maps or in Google Earth to help find the correct heading:
  • GeoLocator tool allows interactive picking of correct heading on a map as part of metadata authoring.

[edit] Use of the information

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:

[edit] Things to do

  • 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.
  • 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 on recently geocoded images (gallery).
  • Find coordinates with unknown headings and try to fix them (see [1]).
  • Replace all usages of {{coord}} and {{coordinate}} with {{Location dec}}. This requires a change in syntax.

[edit] Participants

Geocoded images on Commons

[edit] See also

Retrieved from "http://commons.wikimedia.org/wiki/Commons:Geocoding"
Personal tools