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ideal-postcodes / postcodes.io

UK postcode & geolocation API, serving up open data
https://postcodes.io
MIT License
1.23k stars 245 forks source link

Nearest postcode lookup fails in some cases #34

Closed billinghamj closed 9 years ago

billinghamj commented 9 years ago

I've found a case where coordinates do not resolve to a postcode for some reason. I would expect it to return a postcode in the OL1 outcode:

https://api.postcodes.io/postcodes?lon=-2.0906458&lat=53.5642772

Any idea why this is happening? What could be done to fix it?

Thanks :)

cblanc commented 9 years ago

You can fix this by increasing the search radius. Default is currently 100m, the max is 2000m.

https://api.postcodes.io/postcodes?lon=-2.0906458&lat=53.5642772&radius=500

You'll need to be careful when increasing the radius as this could slow down your queries in densely populated areas.

Alternatively you can use wideSearch=true which can search up to 20km and is fast in urban areas. It uses a naive incremental search to find the nearest points. The tradeoff here is that it returns a maximum of 10 results. Check out postcodes.io/docs under reverse geocoding

If you're wondering why it's returning null and not an empty array, this is bad design on my part. nulls will be fixed whenever there's a v2 of the API but remain for now because too many users depend on this behaviour.

billinghamj commented 9 years ago

Awesome, thank you :)