XQuery/Google Geocoding

Motivation You have one or more geographic names and you want to create a map of these locations. Method We will use a Google RESTful web service to return geographical data from a list of place names. Google provides an HTTP-based Geocoding service. This requires registration of a site for a API key and there are limitations on the usage of this API. Results can be returned in XML or JSON. Querying Google's API The following script takes a location and returns the xml from the service: let $key := "apikey" let $location := request:get-parameter("location",()) let $location := escape-uri($location,false()) let $url := concat("https://maps.googleapis.com/maps/api/geocode/xml?address=",$location,"&key=",$key) let $response := doc($url) return $response </source > ==== Examples ==== Single City Examples: * [http://kitwallace.co.uk/xqbook/geo/googlegeocode.xq?location=Minneapolis Minneapolis] - example using a single city with no country * [http://kitwallace.co.uk/xqbook/geo/googlegeocode.xq?location=Bristol,UK Bristol,UK] - example using a city and country Multiple matches may be returned: * [http://kitwallace.co.uk/xqbook/geo/googlegeocode.xq?location=Bristol Bristol] * or a false positive: [http://kitwallace.co.uk/xqbook/geo/googlegeocode.xq?location=Santas+House Santa's House] In the UK, this service will geocode postcodes: * [http://kitwallace.co.uk/xqbook/geo/googlegeocode.xq?location=BS3+4EA Bristol Hackspace] == Response as KML == The XML response can be reformated as a KML file. Note the addition of the relevant media-type for KML . <syntaxhighlight lang="xml"> let $key := "my apikey" let $location := request:get-parameter("location",()) let $location := escape-uri($location,false()) let $url := concat("https://maps.googleapis.com/maps/api/geocode/xml?address=",$location,"&key=",$key) let $response := doc($url)/GeocodeResponse return if ($response/status="OK") then let $x := response:set-header('Content-disposition',concat('inline;filename="',$location,'.kml";')) let $result := $response/result[1] let $serialize := util:declare-option("exist:serialize", "method=xml media-type=application/vnd.google-earth.kml+xml indent=yes") return <kml> <Folder> <name>{$location}</name> {for $result in $response/result return <Placemark> <name>{string($result/formatted_address)}</name> <Point> <coordinates>{$result/geometry/location/lng/string()},{$result/geometry/location/lat/string()},0</coordinates> </Point> </Placemark> } </Folder> </kml> else $response If you have GoogleEarth, this should load an overlay showing multiple Bristol locations: Bristol KML GoogleMap A simple way to view the generated kml is to use GoogleMaps. This script simply constructs the relevant URL to use the script above and then redirects to that URL: let $location := request:get-parameter("location",()) let $wikiurl := escape-uri(concat("http:/kitwallace.co.uk/geocodekml.xq?location=",$location),false()) let $url := concat("http://maps.google.co.uk/maps?q=",$wikiurl) return response:redirect-to(xs:anyURI($url)) Sadly this approach no longer works with GoogleMap - see support lost Bristol An alternative approach is to use GoogleMap's JavaScript API. Note that to embed JavaScript requires doubling { so it is generally easier to put the Javascript in a separate file. This approach makes use of any existing kml overlay and is simpler, but more restricted than implementing the map using the JavaScript API declare option exist:serialize "method=xhtml media-type=text/html"; let $location := request:get-parameter("location",()) let $url := escape-uri(concat("http://kitwallace.co.uk/xqbook/geo/geocodekml.xq?location=",$location),false()) return <html> <head> <script src="https://maps.googleapis.com/maps/api/js?v=3&key=myapikey"></script> <script type="text/javascript"> function initialize(url) {{ var map = new google.maps.Map(document.getElementById("map_canvas")); var kmlLayer = new google.maps.KmlLayer({{ url: url, map:map }}); }} </script> </head> <body onload="initialize('{$url}')"> <h2>Map of {$location}</h2> <div id="map_canvas" style="height: 80%;width: 80%; margin: 0px; padding: 0px"> </div> </body> </html> Examples * Bristol * London [Setting the zoom level doesn't seem to work] Data to overlay Often the locations are defined in a data file. The following script reads a local file of (a sample of ) whisky distilleries and creates a KML overlay. let $key := "apikey" let $locations := doc("/db/apps/xqbook/geo/whisky.xml") let $serialize := util:declare-option("exist:serialize", "method=xml media-type=application/vnd.google-earth.kml+xml") let $x := response:set-header('Content-disposition','inline;filename=whisky.kml') return <kml> <Folder> <name>Distilleries</name> {for $location in $locations//Whisky let $url := concat("https://maps.googleapis.com/maps/api/geocode/xml?address=",$location/Postcode,"&key=",$key) let $response := doc($url)/GeocodeResponse let $result := $response/result[1] return <Placemark> <name>{$location/Brand/string()}</name> <description>{$location/Address/string()}</description> <Point> <coordinates>{$result/geometry/location/lng/string()},{$result/geometry/location/lat/string()},0</coordinates> </Point> </Placemark> } </Folder> </kml> Whisky overlay and a modified version of the JavaScript can use the output to create a Whisky map