conf

input {
  file {
    path => "/var/log/apache2/access.log.json"
    format => json_event
    type => apache
  }
}

filter {
  geoip {
    source => "client"
    add_tag => [ "geo" ]
#    add_field => [ "geo_json", "%{@soure.longitude}", "geo_json", "%{@source.latitude}" ]
  }

  mutate {
    merge => ["@fields.geo_json", "geoip.longitude"]
    tags => [ "geo" ]
  }

  mutate {
    merge => ["@fields.geo_json", "geoip.latitude"]
    tags => [ "geo" ]
  }

}

output {
  stdout { debug => true }

#  elasticsearch_http {
#    host => "es01.bownty.net"
#  }
}

out.json

{
         "@source" => "file://ip-10-33-129-37//var/log/apache2/access.log.json",
           "@tags" => [
        [0] "geo"
    ],
         "@fields" => {
                 "client" => "77.213.176.86",
          "duration_usec" => 4081,
                 "status" => 200,
                "request" => "/js/bownty.v3.js?v=1370008443",
                "urlpath" => "/js/bownty.v3.js",
               "urlquery" => "?v=1370008443",
                  "bytes" => 6783,
                  "vhost" => "da.bownty.com",
                 "method" => "GET",
               "referrer" => "http://da.bownty.com/?gclid=CPDc15zy8LcCFYF6cAodSwcA_g",
                  "geoip" => {
                        "ip" => "77.213.176.86",
             "country_code2" => "DK",
             "country_code3" => "DNK",
              "country_name" => "Denmark",
            "continent_code" => "EU",
               "region_name" => "",
                 "city_name" => "",
               "postal_code" => "",
                  "latitude" => 56.0,
                 "longitude" => 10.0,
                  "dma_code" => nil,
                 "area_code" => nil,
                  "timezone" => "Europe/Copenhagen"
        },
               "geo_json" => [
            [0] nil
        ],
        "geoip.longitude" => [
            [0] 10.0
        ],
         "geoip.latitude" => [
            [0] 56.0
        ]
    },
      "@timestamp" => "2013-06-19T21:50:18+0200",
    "@source_host" => "ip-10-33-129-37",
    "@source_path" => "//var/log/apache2/access.log.json",
           "@type" => "apache"
}