Using Kibana4 Tile Map with Geo-Points

Question

I'm using Logstash to insert a location attribute into my logs that are going into ElasticSearch:

"location" : {
  "lat":31.07,
  "lon":-82.09
}

I'm then setting up a mapping to tell ElasticSearch it's a Geo-Point. I'm not exactly sure how this call should look. This is what I've been using so far:

PUT logstash-*/_mapping/latlon
{
  "latlon" : {
    "properties" : {
      "location" : {
        "type" : "geo_point",
        "lat_lon" : true,
        "geohash" : true
      }
    }
  }
}

When I query for matching records in Kibana 4, the location field is annotated with a small globe. So far, so good.

When I move to the Tile Map visualization, bring up matching records, bucket by Geo Coordinates, select Geohash from the 'Aggregation' drop down, and then select location from the Field drop down, and press 'Apply', no results are returned.

The aggreations part of the request looks like this:

"aggs": {
    "2": {
      "geohash_grid": {
        "field": "location",
        "precision": 3
      }
    }
  }

And the response:

{
  "took": 5,
  "timed_out": false,
  "_shards": {
    "total": 10,
    "successful": 10,
    "failed": 0
  },
  "hits": {
    "total": 689,
    "max_score": 0,
    "hits": []
  },
  "aggregations": {
    "2": {
      "buckets": []
    }
  }
}

For some reason, ElasticSearch isn't returning results, even though it seems like the Geo-Point mapping is recognized. Any tips for how to troubleshoot from here?