Why embedded URLs should not be used for geotagging

Many previous attempts at SMS geotagging have simply incorporated a Google Maps URL into the message body. While this maximizes the chances that an existing handset can display the location, it has many drawbacks that make it unsuitable as a future geotagging standard.

  • It relies on the receiving device having internet access. That is not a valid assumption. Some might argue that devices without internet access can’t display locations, but that’s not true. Many devices contain pre-installed maps, and others might choose to display the location with, say, a compass needle and distance counter.
  • URLs are verbose. An SMS is limited to 160 characters, so every letter counts. The overhead for a Google Maps URL is http://maps.google.com/maps?q= or 30 characters, versus four characters for geo:. In theory you could set up a shorter URL, but you’d never get down to four characters.
  • URLs change. We think of Google Maps as a permanent part of the internet’s infrastructure, but it’s only been around for five years. Some time in the future Google may go out of business, start charging for the service, or change the syntax.
  • Google Maps URLs have no way to specify altitude or accuracy. Maybe you could set up a different mapping service that does take those parameters, but you’d have to make the website as reliable as Google, available around the clock and able to handle heavy loads.
  • The receiving handset has no discretion over how to display the location. It will be displayed as a pushpin on an English-language Google Map, and that’s it. No way to show your current position as well. No way to show the rest of the geotagged message at the same time. And no way to display the direction and distance to the location.
  • In general, a URL geotag is not unambiguously machine-readable. A parser may do a decent job of extracting the latitude and longitude from a Google Maps URL, but for arbitrary URLs it’s not possible to do this reliably. Why does it matter? Because there are applications where the location has to be processed by a machine. Imagine an SMS-a-Taxi service where you send your desired pickup location. A server on the back end has to be able to parse the location and route the SMS to the nearest available taxi without any human intervention.

The aim of geotagging is to transmit a location, but the function of a URL is to display one, which is a different thing. The URL only contains a view of the location, not necessarily the location itself. It’s the difference between sending someone a fax of a printed document versus e-mailing them the file. The fax might be human-readable, but it’s useless to machines. The file itself can be put to many uses.

So in conclusion, URLs are not suitable as a geotagging standard. If you really want to make sure that a receiving handset can display a location, use a proper geotagging standard such as geosms and include a URL. It’ll cost an extra 20-30 characters, but in the long run it will be more useful to the recipient.


About geosms

A PhD Candidate in Geospatial Sciences, at RMIT's School of Mathematical and Geospatial Sciences.
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1 Response to Why embedded URLs should not be used for geotagging

  1. Pingback: neogeo | GeoSMS

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