I have been having a lot of fun with two Yahoo! technologies that have been evolving quickly. YQL and GeoPlanet. The first, YQL, puts an SQL-like interface on top of all the data on the Internet. And the second, GeoPlanet, introduces the concept of a WOEID (Where-On-Earth ID) that you can think of as a foreign key for your geo-related SQL expressions.

First some example YQL queries to get you used to this concept of treating the Internet like a database. Go to the YQL Console and paste these queries into the console to follow along.

select * from geo.places where text="SJC"

This looks up "SJC" in GeoPlanet and returns an XML result containing this information:

        <woeid>12521722</woeid>
        <placeTypeName code="14">Airport</placeTypeName>
        <name>Norman Y Mineta San Jose International Airport</name>
        <country code="US" type="Country">United States</country>
        <admin1 code="US-CA" type="State">California</admin1>
        <admin2 code="" type="County">Santa Clara</admin2>
        <admin3/>
        <locality1 type="Town">Downtown San Jose</locality1>
        <locality2/>
        <postal type="Zip Code">95110</postal>
        <centroid>
            <latitude>37.364079</latitude>
            <longitude>-121.920662</longitude>
        </centroid>
        <boundingBox>
            <southWest>
                <latitude>37.35495</latitude>
                <longitude>-121.932152</longitude>
            </southWest>
            <northEast>
                <latitude>37.373211</latitude>
                <longitude>-121.909172</longitude>
            </northEast>
        </boundingBox>

The first thing to note is the woeid. It is just an integer, but it uniquely identifies San Jose Airport. If you were to search for "San Jose Airport" instead of "SJC" you would find that one of the places returned has the exact same woeid. So, the woeid is a way to normalize placenames. The other thing to note here is that you get an approximate bounding box. This is what makes the woeid special. A place is more than just a lat/lon. If I told you that I would meet you in Paris next week, that doesn't tell you as much as if I told you that I would meet you at the Eiffel Tower next week. If we pretend that the Eiffel tower is in the center of Paris, those two locations might actually have the same lat/lon, but the concept of the Eiffel Tower is much more precise than the concept of Paris. The difference is the bounding box. And yes, landmarks like the Eiffel Tower or Central Park also have unique woeids. Try it:

    select * from geo.places where text="Eiffel Tower"

Note that the YQL console also gives you a direct URL for the results. This last one is at http://query.yahooapis.com/v1/public/yql?q=select%20*%20from%20geo.places%20where%20text%3D%22Eiffel%20Tower%22&format=xml. Not the prettiest URL in the world, but you can feed that to a simple little PHP program to integrate these YQL queries in your PHP code. Something like this:

    <?php
    $url = "http://query.yahooapis.com/v1/public/yql?q=";
    $q   = "select * from geo.places where text='Eiffel Tower'";
    $fmt = "xml";
    $x = simplexml_load_file($url.urlencode($q)."&format=$fmt");
    ?>

For a higher daily limit on your YQL queries you can grab an OAuth consumer key and use the OAuth-authenticated YQL entry point. There is an example of how to use pecl/oauth with YQL at http://paul.slowgeek.com/hacku/examples/yql-oath.php. Take a close look at the YQL query in that example. It is:

    select * from html where xpath= '//tr//a[@href="https://toys.lerdorf.com/wiki/Capital_(political)"]/../../../td[2]/a/text()'  
     and url in (select url from search.web where url like '%wikipedia%' and query='Denmark' limit 1) 

Sub-selects! So, we do a web search for urls containing the string 'wikipedia' whose contents contains 'Denmark'. That is going to get us the Wikipedia page for Denmark. We then perform an xpath query on that page to extract the text of the link containing the name of the capital of Denmark. Change 'Denmark' in that query to any country and the query will magically return the capital of that country. So, YQL is also a general-purpose page scraper.

But back to the woeid. Places belong to other places, and they are next to other places and they contain even more places. That is, a place has a parent, siblings and children. You can query all of these. Here is a woeid explorer application written entirely in Javascript:

http://paul.slowgeek.com/hacku/examples/geoBoundingBoxTabs.html

Try entering some places or points of interest around the world and click on the various radio buttons and then the "Geo It" button to see the relationship between the places and the bounding boxes for all these various places. If you look at the source for this application you can see that it uses YQL's callback-json output, so there is no server-side component required to get this to work. Try doing a search for "Eiffel Tower" and turn on the "Sat" version of the map. You can see that the bounding box is pretty damn good. Try it for other landmarks. Then walk up the parent tree, or across the siblings. Or check out the Belongs-To data.

Once you have a woeid for a place, you can start using it on other services such as Upcoming:

    select * from upcoming.events where woeid=2487956

and Flickr:

    select * from flickr.photos.search where woe_id=2487956

(yes, I know, it would have been nice if the column names were consistent there)

And finally you can also add YQL support for any open API out there. There is a long list of them here:

http://github.com/spullara/yql-tables/tree/master

To use one of these, try something like this:

    use 'http://github.com/spullara/yql-tables/raw/master/yelp/yelp.review.search.xml' as yelp; 
    select * from yelp where term='pizza' and location='sunnyvale, ca' and ywsid='6L0Lc-yn1OKMkCKeXLD4lg'

As a bit of Geo and API nerd, this is super cool to me. I hope you can find some interesting things to do with this as well. If you build something cool with it, please let me know.