title: Difference between $center and $centerSphere in Mongo?
body: <p>Currently, we are using $centerSphere to find nearby cities. One example is that for the locality Bee Cave in Texas, USA, $centerSphere correctly found the only city Austin in a radius of 30 kilometers (As per documentation, it was converted in <strong>radians</strong>). Now, for the city Lautoka in Fiji (Lat: -17.6169618, Long: 177.4504609) it is giving the error "Spherical distance would require (unimplemented) wrapping". This is question one: what does this error mean?</p>
  
  <p>We tried implementing the same by using $center. I'm aware we need to give distance in miles rather than radians. After implementing, for Bee Cave, I got US cities that were thousands or hundreds of miles away. One example is Albuquerque. I'm unable to understand why these cities are coming even after following Mongo documentation properly. </p>
  
  <p>I'm using the query (for Bee Cave, TX)</p>
  
  <pre><code>db.places.find{
     "geo": {
        $geoWithin: { $center: [ [ -97.9524, 30.3061 ] , 18.64 ] }
     }
  }
  </code></pre>