Your Place Is Not My Place; The Perils of Disambiguation

We take the art of geographic lookup for granted these days; type a place name into a form on a web site or feed it into a web service API and hey presto! Most of the time you’ll be told whether or not the place name is valid or not and, in case there’s more than one place with the same name, either asked to choose which one you mean or be presented with the most likely place.

Most of the time … but not all of the time.

Which Way To The Town Centre?

The hey presto bit of the process seems at first glance to be relatively trivial but isn’t. Just ask anyone who’s had to implement a system that handles place names. Actually, the hey presto part is actually two discreet processes in their own right. First of all we need to identify a place, or whether indeed there’s a place at all; this is usually called geoidentification.

identify; verb; establish or indicate who or what (someone or something) is

This is the thing that determines that there is a place in “I’m in London today” but not in “I do love Yorkshire Pudding“.

Once a place has been identified, we need to work out if there’s more than one place of the same name (which is more than likely as we’re stunningly unimaginative where place names are concerned, duplicating and reusing the same name all over the world) and if so, which one. This is usually called geodisambiguation.

disambiguate; verb; remove uncertainty of meaning from (and ambiguous sentence, phrase or other linguistic unit)

Some places are pretty easy to disambiguate; as far as I know there’s only one Ouagadougou and that’s the capital of Burkina Faso. Some places should be easy to disambiguate, least at first sight; take London, that should be easy. It’s the capital of the United Kingdom. Well that’s true but it could also be the London in Ontario, or the one in Arkansas, in California, in Kentucky or any of the other 22 Londons that I’m aware of.

The gentle art of disambiguation is critical to the act of geocoding, geoparsing, geotagging and any of the other words the the location industry chooses to tack geo on as a prefix. Get disambiguation wrong and you fail on two counts.

Firstly, you’re showing your audience that you don’t know or don’t care about what they’re trying to tell you. Secondly, you allow your users the opportunity to specify the same place in a multitude of conflicting ways.

This is part of the problem of GeoBabel; your place is not my place.

So far, so theoretical, but let’s look at a concrete example of this. A few weeks back I added my Twitter account to the Twitter directory site The first thing you’re asked to do is to supply your location, or to “Type Your City” as phrases it. So I type London and the site starts to attempt to disambiguate on the fly; so do I mean “London, United Kingdom” or “London, Ontario“? But wait, what about the other options? - London geo disambiguation fail #1

Which “London” is the one tagged by 436 people but with no indication of which country? What’s the difference between “London, United Kingdom“, “London,UK” and “London England“. Space and punctuation, or the lack of it, is obviously important to here. So let’s try and give the system some help and start to type United Kingdom … - London geo disambiguation fail #2

Oh dear. The “London, United Kingdom” still shows up but because I’ve put a space in there I don’t get offered “London,UK” anymore but I do get offered the London in the lesser known country of “Uunited Kingdom” and also “London, Ub2“, which one assumes is the UB2 postal code which specifies the London suburb of Southall.

Your place is not my place.

To be fair, I’m not singling out for attack here; this is just one of many examples of sites who try to use geographic lookup but end up making life difficult for their users (but which London do I pick?) and for themselves (now, how many users in London in the UK do we have?). I’d happily offer to help them; if only I could find any contact information anywhere on the site …

Photo Credits: foilman on Flickr.
Written and posted from the Yahoo! London office (51.5141985, -0.1292006)

Written by Gary

A self-professed map addict, Gary has worked in the mapping and location space for over 20 years through a combination of luck and occasional good judgement. Gary is co-founder of Malstow Geospatial, which provides handmade, professional geospatial consulting. A Fellow of the RGS, he tweets about maps, writes about them...
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john fagan

From when i last looked (while working on this problem at Bing), 20% of UK places share the same name, and about 50% in USA!

Ranking data to find best match using traditional methods, such as population or tags works 90% of the time, bringing in context meta-data can improve on that, such as users reverse ip, current map view etc.. Maybe there is opportunities in a PlaceRank algorithm, using a number of data sources, including social data, web crawling, spatial relationships, real time data. A place can be important one day and not the next!

Stu Mitchell

I think the other issue here is, what do you use as the correct parent geography as ‘discriminator’: London, UK vs. London Ontario makes sense (‘State’/’Country’), but what happens when you get two in the same parent? If I choose ‘Newport’, I need ‘County’ to discriminate between ‘Gwent’ and ‘Shropshire’, for instance.

Near me is a village called ‘Newbiggin’. However, there are 3 in my county (North Yorkshire). Streetmap, for instance, lists all of these, but only with county name, so I need to view each on the map before I choose the correct one.

Size/significance, proximity and other context may help. In he end, a small thumbnail map might be the only way to avoid the old ‘try each one’ route.

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