Much has been written about the utility of geotagging – meaning the attribution of location or extent to a web page. This essential bit of metadata was part of the original Dublin Core proposals along with author, title and so forth. Like many other pieces of metadata it has so far not gained a great deal of currency. With the advent of "local search" and the geo-enabling of the various search engines – this may change in the next couple of years.
To geo-tag a web pag is simple enough. One can simply add a new metadata tag that contains a location. This can be specified by a GML point, or other geometry, or by referencing a feature (e.g. Eiffel tower). Without being concerned with the syntax at this point, how much does this really do for us?
For some types of web pages this makes perfect sense. The original "coverage" attribute in DC had this in mind. If I write a web page which is the history of France then it is clear that a geotag indicating "France" is meaningful. But anything more complex and things are not so clear.
If my web page concerns multiple places – does it help to attach geo-tags for all of the places that I reference?
If my web page is concerned with ordering physical goods, I might want to know the location of the store, warehouse or pickup depot. These can be referenced within the web page for sure – and some means of indicating their location is clearly useful. But this is then no longer related to the web page and is just geographic information "in the page"
So while geo-tagging in the sense of web page metadata has rather limited uses – the use of geographic information – encoded within a web page, can have significant benefits.
A web page describing a flood, earthquake or other natual disaster could contain geographic data or data references that could then be visualized as SVG or other graphics within the web page. This could include animation or even user interaction with the information.
A web page selling physical goods could contain location information that could be combined with the readers current location (e.g. via GPS, cell zone) to providing routing instructions to the store, depot or warehouse.
Note that the information could be in-line within the web page – or can be supplied by means of references to geographic information located in an online web service such as an OGC-compliant Web Feature Service.
We will explore the syntax of this using GML in the next article.