Why are some geo tagged tweets null? (Twitter Streaming API)

I'm using the twitter streaming api to gather tweet locations from around the world. I'm receiving plenty of live tweets but some of the geo tags are null.

I'm using the statuses/filter api with the following url:

http://stream.twitter.com:80/1/statuses/filter.json?locations=-180,-90,180,90

This url returns tweets, some of the geo json fields are null. Has anyone else experienced this? Or have ideas on why?

Roughly only 60% of all the tweets returned by the said url return valid (non null) lat lon locations.

Thanks.

edit: If you go to the url (after logging in with twitter account info), you can see what I'm talking about.

Just search for 'coordinates' or 'geo'.

Something else I've noticed, is that there is a 'geo_enabled' tag and a 'geo' t开发者_C百科ag. I wonder if the locations filter is returning all of the "geo_enabled":true tweets. If you look hard enough you might can find a "geo":null tag.

Any thoughts on this?

The Streaming API matches against geo, coordinates, and place. You can see the place parameter in the sample status I pulled from the stream below.

{
    "geo": null,
    "coordinates": null,
    "place": {
        "country_code": "US",
        "bounding_box": {
            "type": "Polygon",
            "coordinates": [[[ - 77.119759, 38.791645], [ - 76.909393, 38.791645], [ - 76.909393, 38.995548], [ - 77.119759, 38.995548]]]
            },
        "place_type": "city",
        "country": "United States",
        "attributes": {},
        "full_name": "Washington, DC",
        "name": "Washington",
        "url": "http:\/\/api.twitter.com\/1\/geo\/id\/01fbe706f872cb32.json",
        "id": "01fbe706f872cb32"
    },
    "user": {
    },
    "id": 73218362645282816
}