This is usually done with a GPS receiver which may be built into the camera or carried around separately. Apple's iPhoto is just one of a number of programs which can then display the location on a map.
GPS receivers work by establishing communication with a network of satellites orbiting the earth and using the principle of triangulation to work out their precise position from the signals received from these satellites.
There are some problems with in-camera GPS systems, though:
• They use power all the time they're on
• Older GPS systems can take a little time to lock on to the GPS satellites
• GPS doesn't work indoors and can be unreliable outside if you're surrounded by tall buildings or trees etc. The other two issues are likely to be resolved by improved camera design, but the connectivity looks like it will continue to be an issue. As a result, you may find you come back from a trip with some of your photos tagged but not all of them.
Geotagging information is stored within the image file as a pair of co-ordinates using the longitude and latitude system employed by geographers and navigators for centuries. You can find it alongside the image's other EXIF data, which includes things like the date the picture was taken, shutter speed, lens aperture, ISO and so on. Below you can see the GPS information at the bottom of the metadata panel in Lightroom.
But having the location’s co-ordinates is not the same as knowing the name of the place or the district or the country. For this you need some kind of ‘mapping’ tool, and this usually means using a computer and a program like Google Earth. What you do here is 'drop' your photos on to a map (see below), and this simultaneously assigns these map co-ordinates to the image file.
Ideally, though, it would be better to have the camera insert the location automatically as you take the photo, and this means building in some kind of positioning system. The obvious solution here is a built-in GPS receiver. After all, these have proved extremely effective for in-car satellite navigation systems. GPS receivers aren't completely foolproof, though; they don't work well indoors, for example, and tall buildings or forests can cause problems. They also draw a certain amount of power.
Nikon makes a GPS receiver which clips to the accessory shoe of its digital SLRs, and has built GPS into its P6000 compact. The limitation here is that the camera records the co-ordinates but not the country or place name, and some kind of mapping tool is required later to put a name to the place.
However, Samsung's ST1000 compact (above) takes the technology a step forward by incorporating its own mapping system, so that the camera not only records the GPS co-ordinates but the names of cities too.
Cameras with built-in GPS may become more common in the future, but until then there are two ways to geotag your photos.
One, as we've seen, is to use a program like Google Earth where you manually ‘pin’ untagged photos to a map, which then embeds the latitude and longitude data in the image. It’s crude but effective and easy enough to understand.
The other, more technical solution is to use a separate GPS device or GPS ‘logger’. First, you synchronise the GPS device’s clock with the camera’s, then carry it everywhere you take the camera. Later, you can use GPS logging software to synchronise the GPS log with the digital camera’s images, again embedded them positional data in the photos.
But although geotagging can be problematic, if you're prepared to get more heavily into the technicalities there's a lot you can do to make it a more reliable and more useful process. Take a look at this site, suggested to use by Sebastian Hofer. It's in German, but the Google Translate button at the top right will turn it into perfectly legible English.
