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A lot of career websites allow you to select jobs from within a radius of your chosen location.

Since cities and towns can be considered irregular in shape, sprawling in the definition (do you discount outer suburbs etc.).

How is the centre of a city defined? And is it the same as the location used as described above?

closed as too broad by PolyGeo Jan 9 at 19:28

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    This question is very specific but they calculate the centroid of the polygon. en.wikipedia.org/wiki/Centroid – Pete Jan 9 at 15:32
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    It seems that your question is really "how are city boundaries defined?" The centroid calculation is quite simple as Pete mentioned. Interestingly, for a really oddly-shaped city, it's possible for the centroid to lie outside of the city boundaries. But I can't think of any examples where this is actually the case. – Jon Jan 9 at 15:42
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    I believe your question goes beyond simple geographical location, as Pete and Jon mentioned, there are many ways to find out the centroid of a polygon, even irregular shape polygon. Though, for some location based engines such as job search, the center of city are chosen based on many factors, including distance to the city boundary, population, economy etc. – MaxG Jan 9 at 19:24
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    I think this will depend on the website and the GIS software that it is using. Some may use Euclidean distance from GPO (General Post Office). – PolyGeo Jan 9 at 19:30
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    I absolutely agree with what @MaxG has said. In my opinion, the city centre is not only and always the geocentroid, but can be another place that played a key role in forming the city, one of those was particularly mentioned by PolyGeo, i.e. General Post Office. However, there are many other POIs that could be taken into consideration as a city centre, e.g. city's main square, city hall or administration, main church, railway station, port etc. – Taras Jan 10 at 7:05