Using Twitter's Streaming API. Selecting Geohash Aggregation 'filters' all fields out but geoip.location which does not 'map' tweets for me. I think information needed lies in coordinates.coordinates but this does not show as geo type. Kibana 3 used to allow this some time ago. Could be Twitter change as well I guess. Any idea? 
I described what I had to do with Logstash here. Search for Twitter tracking in the page.
You will see the index template I defined for this purpose.
Hope this helps.