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a-small-toy-to-explore-geohashes.html
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<h1><a href="/2011/09/a-small-toy-to-explore-geohashes">A small toy to explore geohashes</a></h1>
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<p>For an app I've been building, I've been looking into <a href="http://geohash.org/">geohashes</a>. For those who don't know, the <a href="http://en.wikipedia.org/wiki/Geohash">geohash</a> format is a simple way to encode latitude and longitude into a single string. As an example, Nelson's Column in London (51.507794, -0.127952) has the geohash <code>gcpvj0dyds</code>.</p>
<p>Geohashes have a couple of interesting features. First, as you remove characters, you lose precision. <code>gcpvj0dyds</code> fairly accurately points to Nelson's Column; <code>gcpvj0d</code> represents the South-West of Trafalgar Square and some of the Mall; and <code>gcpvj</code> covers most of Central London, as well as Islington and King's Cross. A geohash doesn't really represent a point, but rather a bounding area within which a point may lie. The longer the geohash, the smaller that bounding area.</p>
<p>The other interesting property geohashes have is that nearby locations usually (but not always) share similar prefixes. So much of North London is in <code>gcpv</code>, while much of South London is in <code>gcpu</code>. However, due to the <a href="http://en.wikipedia.org/wiki/Prime_Meridian">Prime Meridian</a> passing through Greenwhich, South East London has the geohash <code>u10h</code> - wildly different than the other two.</p>
<p>This probably sounds a bit complicated. I was having trouble getting my head around the concept, so to try and get to grips with geohashes I've written a toy app that draws them on a map. To try it out, go to <a href="http://geohash.gofreerange.com">http://geohash.gofreerange.com</a>, click the map, zoom and play. If you find it useful, let me know.</p>
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Update: This code is now available [on github](https://github.com/tomafro/geohash-explorer).
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<span class='author'><a rel='author' href='http://tomafro.net'>Tom Ward</a></span>
<span class='date'><a href="/2011/09">15th September 2011</a></span>
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<li><a href="/tags/geohash" rel="tag">geohash</a></li>
<li><a href="/tags/toy" rel="tag">toy</a></li>
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