How GPS Photo Taggers Work

Mechanics of GPS Photo Taggers

You have to make your EXIF data visible in Flickr if you want your GPS tags to show up.
You have to make your EXIF data visible in Flickr if you want your GPS tags to show up.
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When you take a photo with a digital camera, the camera records a lot more data than just the image. This information includes the time and date when the photo was taken, the orientation of the camera (portrait or landscape), whether a flash was used and even detailed camera settings like aperture, exposure and focal length. All of these data is stored in something called the EXIF header of the photo.

EXIF stands for Exchangeable Image File Format. EXIF headers provide a way of stamping photos with data that can read by other applications like photo management software or photo Web sites. This is how your computer automatically knows to put your photo in a folder titled February 28, 2009, and to rotate the image 90 degrees.

The cool thing about EXIF headers is that there's room to include longitude, latitude and altitude coordinates. In recent years, we've seen new hardware and software applications that can embed location data into EXIF headers using GPS technology.

To understand how this works, we'll walk you through the process for manually GPS tagging a photo using a standard digital camera and an inexpensive GPS receiver.

  1. Turn on your GPS receiver and your digital camera. Make sure that the clock on your camera is set to the same exact time as the clock on your GPS receiver.
  2. Set your GPS receiver to "tracking" or "log" mode. Your receiver will now record a running log of your location over a period of time.
  3. Carry your GPS receiver in a backpack or in your pocket as you take pictures throughout the day.
  4. After you upload your pictures to your computer, select the photos you want to tag with GPS coordinates. Note the exact time that each picture was taken (most photo management software will display this information).
  5. Go to your GPS tracking log. Write down the GPS coordinates associated with the time of each photo.
  6. Use EXIF editing software to enter the GPS information into the EXIF header of each photo.

Manually tagging each photo with GPS coordinates can be a bit labor-intensive. Also, even though there are plenty of free and shareware EXIF editors available online, there isn't a surefire solution that works every time on every operating system. As of this writing, iPhoto '09 from Apple is the only mainstream photo editing software that lets you manually add GPS coordinates to an EXIF header [source: Shankland].

Luckily, there are plenty of new hardware, software and Web applications that make it easy to tag your photos with GPS data and share them on interactive, online maps. Keep reading to learn more.