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Getting a Precise Location in Bing Maps

Before this release, the Bing Maps geocoding engine used a common and simple interpolation scheme. In essence, if the geocoding engine knew that the 1300 block of Main Street started at position (X1,Y1) and ended at (X2,Y2), then 1325 Main Street must be 1/4 of the way between those two points. While useful, that technique can often return results that are imprecise, particularly in areas where homes are not evenly spaced.

Developers who wanted more precise geocoding had an option, which is to use the MapPoint Web Service (MWS) to get the precise location of a street address, as described in the Precise Geocoding with MapPoint Web Service and Bing Maps article.

This release of the Bing Maps AJAX Control 6.3 has a number of upgrades, including improved geocoding for the UK and Canada, improved address parsing, and a unified geocoding layer built into the Bing Maps backend architecture that allows multiple address parsers and geocoding engines to be leveraged in order to return the most accurate information available, all through a call to the VEMap.Find method. This article looks at the new functionality available to developers in Bing Maps 6.3 by developing a sample application that explores the geocoding functionality.

Displaying a Map

Geocoding functionality is exposed through the Find method of the VEMap class, so we’ll start by creating a map. The following code is boilerplate HTML and JavaScript to load a map. Save this code as GeoCodeTest.htm, we’ll be adding to it as we go along.

<html xmlns="http://www.w3.org/1999/xhtml" >
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
      <title>Geocoding in Bing Maps</title>
      <script type="text/javascript" src="http://ecn.dev.virtualearth.net/mapcontrol/mapcontrol.ashx?v=6.3"></script>

      <script type="text/javascript">
         var myMap = null;
    
         function LoadMap()
         {
            myMap = new VEMap("mapDiv");
            myMap.LoadMap();
         }
      
         function UnloadMap()
         {
            if (myMap != null) {
               myMap.Dispose();
            }
         }
      </script>
   </head>
   <body onload="LoadMap()" onunload="UnloadMap()">
      <div style="position:relative;width:640px;height:480px;" id="mapDiv" />
   </body>
</html>

If you open this file in your browser, you should see something like the following.

Cc161074.ff0b4ce8-3b35-4fdb-946b-9a6f94fe1fae(en-us,MSDN.10).png

Finding the Address

The first step is to define the parameters necessary for the VEMap.Find method. With 11 different arguments, including an optional callback, and a couple of different modes of use, it is easily the most complicated function in the Bing Maps AJAX Control 6.3 API As such, it’s worth taking a couple minutes to take a close look.

The function signature follows and a description of the various arguments follows, particularly as pertains to geocoding.

VEMap.Find(what, where, findType, shapeLayer, startIndex, numberOfResults, showResults, createResults, useDefaultDisambiguation, setBestMapView, callback);

Parameter Description

what

A string containing the name of the business or entity for which the search is conducted. Either this parameter or the where parameter must be supplied. Since we are looking for an address, we set this parameter to null.

where

A string containing the address for which the search is conducted.

findType

The only currently supported value is VEFindType.Businesses. Since this parameter is optional, we set this parameter to null.

shapeLayer

A reference to a VEShapeLayer object for a what search. Since this parameter is optional, we set this parameter to null.

startIndex

An optional parameter only used for a what search. We set this parameter to null.

numberOfResults

An optional parameter only used for a what search. We set this parameter to null.

showResults

A Boolean value that specifies whether the results are shown on the map. Since where search results are shown automatically only under specific circumstances, so we specify false here and handle the display manually through the callback function.

createResults

A Boolean value that specifies whether pushpins are created. Since where search results are not created anyway, we will specify false here and create the pushpins through the callback function.

useDefaultDisambiguation

A Boolean value that specifies whether to display a disambiguation dialog box if there is ambiguity in the city, state, or country. If this parameter is false the IP address of the user is used to help disambiguate the address. We set this parameter to false.

setBestMapView

A Boolean value that specifies whether to re-centered the map and zoom to the best view of the results of the geocode. We set this paramter to true.

callback

A string containing the name of the function that is called when the search is complete. We set this paramter to GeocodeCallback.

The following example shows the resulting Find call in our StartGeocoding function.

function StartGeocoding( address )
{
   myMap.Find(null,    // what
              address, // where
              null,    // VEFindType (always VEFindType.Businesses)
              null,    // VEShapeLayer (base by default)
              null,    // start index for results (0 by default)
              null,    // max number of results (default is 10)
              null,    // show results? (default is true)
              null,    // create pushpin for what results? (ignored since what is null)
              null,    // use default disambiguation? (default is true)
              null,    // set best map view? (default is true)
              GeocodeCallback);  // call back function
}

Handling the Results

When the Find method has finished its request, it does not report the results through a return value. Instead, it invokes the callback function you have specified. That function has the following signature:

Callback(shapeLayer, findResults, places, moreResults, errorMsg);

Just like with the Find method, these parameters have specific semantics when it comes to geocoding, so let’s look a little more closely at them.

Parameter Description

shapeLayer

A reference to the same VEShapeLayer object as specified in the Find call. Since that parameter was null, this parameter should also be null, so we ignore it.

findResults

This parameter should be null since we set the corresponding paramter to null in the Find call, so we ignore it.

places

An array of VEPlace objects representing the geocoding results, and ordered so that the best match comes first. If there are no matches, this parameter is null.

moreResults

This parameter should be null since we set the corresponding paramter to null in the Find call, so we ignore it.

errorMsg

A string containing any error information from executing the geocoding request. It should be null.

As you can see we ignore all but the third and fifth parameters, places and errorMsg, respectively.

function GeocodeCallback (shapeLayer, findResults, places, moreResults, errorMsg)
{
   // if there are no results, display any error message and return
   if(places == null)
   {
      alert( (errorMsg == null) ? "There were no results" : errorMsg );
      return;
   }

   var bestPlace = places[0];
   
   // Add pushpin to the *best* place
   var location = bestPlace.LatLong;
   
   var newShape = new VEShape(VEShapeType.Pushpin, location);
   
   var desc = "Latitude: " + location.Latitude + "<br>Longitude:" + location.Longitude;
   newShape.SetDescription(desc);
   newShape.SetTitle(bestPlace.Name);
   myMap.AddShape(newShape);
}

Testing the Code

We can perform a simple test by adding a call to the StartGeocoding function in the LoadMap function, which is the function that is called as soon as the body of the HTML page is loaded, as follows.

function LoadMap()
{
   myMap = new VEMap("mapDiv");
   myMap.LoadMap();
   
   StartGeocoding("1 Microsoft Way, Redmond WA");
}

Here is the resulting map.

Cc161074.889c8bf5-d713-4a57-a390-ad528cecc4b1(en-us,MSDN.10).png

Notice how the address displayed in the screen shot has more information (the zip code) than we provided in the code sample. That is because the geocoding engine works to rationalize and fill out the address as part of the process, and it gets returned to you as part of the results. As we shall see shortly, the engine might return multiple possible results, in which case it is useful to know what the rationalized addresses for those different results might be.

Making our Code Interactive

It is not too useful to have the address hardcoded, so before going much further, let’s add the functionality necessary to input an address. First we add a text box in which we can input the address into and add a button to start the geocoding. Change the body section of your HTML to look like the following.

<body onload="LoadMap()" onunload="UnloadMap()">
   <div style="font-family:Arial; font-size:10pt">
      Address: 
      <input id="txtWhere" type="text" style="width:255px" />&nbsp;
      <input type="button" value="Geocode" onclick="onGeocodeClick()" />
   </div><br />

   <div style="position:relative;width:640px;height:480px;" id="mapDiv"></div>
</body>

The button to start the geocoding invokes the onGeocodeClick function, so add that function, as follows.

function onGeocodeClick()
{
   myMap.Clear();
   address = document.getElementById("txtWhere").value;
   StartGeocoding(address);
}

Since we no longer need the hardcoded address test in loadMap, remove it, as follows.

function LoadMap()
{
   myMap = new VEMap("mapDiv");
   myMap.LoadMap();
}

Now you can load your page, input an address and see the result on the map. Notice how Bing Maps geocoding can handle a lot more than just simple addresses, as shown in the following map.

Cc161074.479805ed-e285-411f-8bb7-3c69e142da25(en-us,MSDN.10).png

Digging Deeper Into the Results

So far we only display the first, and hopefully the best, match for the address, but a Find call often returns more than one result. Sometimes those results vary based on the sort of interpolation used (rooftop versus standard), or they can vary based on different interpretations of the address that is supplied, or they could be results from different geocoding engines. Now that we have seen the basic process of geocoding, it is interesting to dig a little deeper into the results we get back.

We start by adding a bit of HTML to our sample application that will give us a place to show the different results. Change the body tag to look like the following.

<body onload="LoadMap()" onunload="UnloadMap()">
   <div style="font-family:Arial; font-size:10pt">
      Address: 
      <input id="txtWhere" type="text" style="width:255px" />&nbsp;
      <input type="button" value="Geocode" onclick="onGeocodeClick()" />
   </div><br />
   
   <div style="position:relative;width:400px;height:400px;" id="mapDiv"></div>
   
   <div id="resultsDiv" style="font-family:Arial;font-size:8pt;position:relative; top:-400px;left:425px;width:400px"></div>
</body>

Next, add some string constants we will use to describe the quality of the geocode results.

var confidenceStrings = [ "High", "Medium", "Low" ];
var precisionStrings = [ "Interpolated", "Rooftop" ];

And the references for different icons for various quality of geocodes, as follows.

var pushpinUrls = ["pushpinGreen.gif", "pushpinOrange.gif", "pushpinRed.gif"];

Here are these pushpins.

Cc161074.4c638cba-74bd-45a8-b0dc-0146cec4e4d3(en-us,MSDN.10).pngCc161074.33288e9e-13e1-4a10-b42f-0e8e774824e5(en-us,MSDN.10).pngCc161074.0b57e919-fcd6-4191-a622-eee630b23058(en-us,MSDN.10).png

Add some CSS to help manage putting text on top of the icons.

<style type="text/css">
   .pinText
   { 
      position:relative; 
      top:-25px; 
      left:2px;
      width:30px;
      color:#ffffff; 
      text-align:center; 
      font: bold 12px Arial; 
   }
</style>

The VEPlace class includes a lot of information, including Precision (rooftop or interpolated) and Confidence (High, Medium or Low). Update the GeocodeCallback function to output the results into the resultsDiv and add confidence and precision information for each pushpin, as follows.

function GeocodeCallback(shapeLayer, findResults, places, moreResults, errorMsg)
{
   var resHtml = "";

   // if there are no results, display the error message and return
   if (places == null)
   {
      alert( (errorMsg == null) ? "There were no results" : errorMsg );
      return;
   }

   // Create an entry for each VEPlace in the result set
   for (var p = 0; p < places.length; p++)
   {
      // Gather some info up front
      var place = places[p];
      var location = place.LatLong;
      var confString = confidenceStrings[place.MatchConfidence];
      var precString = precisionStrings[place.Precision];
      
      // create the info box description
      var desc = "Latitude: " + location.Latitude + "<br/>" +
                 "Longitude: " + location.Longitude;
      desc = desc + "<br>Confidence: " + confString;
      desc = desc + "<br>Precision: " + precString;
      
      // Create a pin at that location, list the latitude & longitude
      var pin = new VEShape(VEShapeType.Pushpin, location);
      pin.SetCustomIcon("<img src='" + 
                        pushpinUrls[place.MatchConfidence ] + 
                        "'><span class='pinText'>" + 
                        (p+1) + 
                        "</span>");
      pin.SetTitle(place.Name);
      pin.SetDescription(desc);
      myMap.AddShape(pin);
      
      // Add the information to the resultsDiv html, including a link 
      // that recenters the map over the pin
      resHtml = resHtml + 
                "<p><a href='javascript:myMap.SetCenter(new VELatLong(" +
                location.Latitude +
                "," +
                location.Longitude +
                "));'>";
      resHtml = resHtml + 
                "#" + (p+1) +
                ": " + place.Name +
                " (" + precString +
                ", " + 
                confString +
                " confidence)</a></p>";
   }
   
   // set the resultsDev html when we're done.
   document.getElementById("resultsDiv").innerHTML = resHtml;
}

The VEPlace object also includes match type information and we will get to that next. For now, you can use this code to test the geocoding results for address. You will see how there are a number of different results that come back from a query, especially an ambiguous one. You even get some you might not expect, as shown in the following map result.

Cc161074.c1d67c70-4ed0-4b26-bfa5-a0ff7916074f(en-us,MSDN.10).png

Additional Geocoding Information

The VEPlace object's MatchCode property includes information about the type of geocoding match that is available. It can also provide an insight into how the geocoding result was found.

The MatchCode property consists of bitmap values.

MatchCode Property Value Description

None

No match was found

Good

A good match was found

Ambiguous

The match was ambiguous

UpHierarchy

A match was found by a broader search

Modified

A match was found, but to a modified place

If a match is found, any of the three latter values can be set in the MatchCode property. To interpret the match information, add the following function to the sample.

function MatchCode(code)
{
   if(code == VEMatchCode.None) {
      return "No match";
   }
   
   var codeDesc = "";
   
   if(code & VEMatchCode.Good > 0) {
     codeDesc += "Good ";
   }
   
   if(code & VEMatchCode.Ambiguous > 0) {
     codeDesc += "Ambiguous ";
   }
   
   if(code & VEMatchCode.UpHierarchy > 0) {
     codeDesc += "UpHierarchy ";
   }
   
   if(code & VEMatchCode.Modified > 0) {
     codeDesc += "Modified ";
   }
   
   return(codeDesc + "Match");
}

Update the GeocodeCallback function to include that information.

// create the info box description
var latitude = location.Latitude;
var longitude = location.Longitude;
var mcVal = MatchCode(place.MatchCode);

var desc = "Latitude: " + latitude + "<br>" +
           "Longitude: " + longitude;
desc = desc + "<br>Confidence: " + confString;
desc = desc + "<br>Precision: " +precString;
desc = desc + "<br>Match Code: " + mcVal;

Also add this information to the resultDiv along the side.

resHtml = resHtml + 
          "<p><a href='javascript:myMap.SetCenter(new VELatLong(" +
          latitude +
          "," +
          longitude +
          "));'>";
resHtml = resHtml + 
          "#" +
          (p+1) +
          ": " +
          place.Name +
          "<br>&nbsp;(" +
          precString +
          ", " +
          confString +
          " confidence, " +
          mcVal +
          ")</a></p>";

You should get results similar to the following.

Cc161074.676219e6-3315-4968-83f5-f7afcc46fda5(en-us,MSDN.10).png

In the example above, you can see some keywords that will help provide context into how the geocode was found.

Modified refers to a match that was found by making educated changes to the input address. In our example, we only provided 8450 161st, Redmond, WA and it changed that to 8450 161st Avenue NE.

Uphierarchy refers to a match that was found by searching on less data Again, in our example, we started with 8450 161st, Redmond, WA and it attempted a match on 161st Place NE, specifying just the street and not the specific address.

Comparing Bing Maps Results with Bing Maps SOAP Services Results

If you search for the two addresses in the Precise Geocoding with MapPoint Web Service and Bing Maps article (10880 Wilshire Blvd Ste 1101, Los Angeles, CA 90024-4112 and 1300 Saratoga Ave Unit 701, Ventura, CA 93003-6407), you get essentially the same results, with much less work.

Conclusion

The MapPoint Web Service has access to a powerful geocoding infrastructure that makes available a level of precision previously only available from the Bing Maps AJAX Control 6.3 using behind-the-scenes requests. Bing Maps AJAX Control 6.3 now exposes this information through the Find method, which invokes a callback function and returns an array of VEPlace objects, which include:

  • A complete address

  • Latitude and Longitude

  • A measure of confidence

  • The type of match (rooftop or interpolated)

  • Information about how the match was reached, such as by modifiying the address

In addition, there can be multiple locations for each match result. These were not covered in this article, but they can be useful for comparing the difference between rooftop and interpolated results.

This article was written by Jeff House. Jeff is a software architect at Advaiya.

Complete Code Listing

Here is the complete code listing.

<html xmlns="http://www.w3.org/1999/xhtml" >
   <head>
      <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
      <title>Geocoding in Bing Maps</title>
      <script type="text/javascript" src="http://ecn.dev.virtualearth.net/mapcontrol/mapcontrol.ashx?v=6.3"></script>

      <script type="text/javascript">
         var myMap = null;
         
         var confidenceStrings = ["High", "Medium", "Low"];
         var precisionStrings  = ["Interpolated", "Rooftop"];
 
         var pushpinUrls       = ["pushpinGreen.gif", "pushpinOrange.gif", "pushpinRed.gif"];
    
         function LoadMap()
         {
            myMap = new VEMap("mapDiv");
            myMap.LoadMap();
         }
      
         function UnloadMap()
         {
            if (myMap != null) {
               myMap.Dispose();
            }
         }
         
         function StartGeocoding(address)
         {
            myMap.Find(null,         // what
                  address,           // where
                  null,              // VEFindType (always VEFindType.Businesses)
                  null,              // VEShapeLayer (base by default)
                  null,              // start index for results (0 by default)
                  null,              // max number of results (default is 10)
                  null,              // show results? (default is true)
                  null,              // create pushpin for what results? (ignored since what is null)
                  null,              // use default disambiguation? (default is true)
                  null,              // set best map view? (default is true)
                  GeocodeCallback);  // call back function
         }
         
         function GeocodeCallback(shapeLayer, findResults, places, moreResults, errorMsg)
         {
            var resHtml = "";

            // if there are no results, display the error message and return
            if (places == null)
            {
               alert( (errorMsg == null) ? "There were no results" : errorMsg );
               return;
            }

            // Create an entry for each VEPlace in the result set
            for (var p = 0; p < places.length; p++)
            {
               // Gather some info up front
               var place = places[p];
               var location = place.LatLong;
               var confString = confidenceStrings[place.MatchConfidence];
               var precString = precisionStrings[place.Precision];
               var mcVal = MatchCode(place.MatchCode);
               var latitude = location.Latitude;
               var longitude = location.Longitude;
      
               // create the info box description
               var desc = "Latitude: " + latitude + "<br/>" +
                          "Longitude: " + longitude;
               desc = desc + "<br>Confidence: " + confString;
               desc = desc + "<br>Precision: " + precString;
               desc = desc + "<br>Match Code: " + mcVal;
      
               // Create a pin at that location, list the latitude & longitude
               var pin = new VEShape(VEShapeType.Pushpin, location);
               pin.SetCustomIcon("<img src='" + 
                                 pushpinUrls[place.MatchConfidence] + 
                                 "'><span class='pinText'>" + 
                                 (p+1) + 
                                 "</span>");
               pin.SetTitle(place.Name);
               pin.SetDescription(desc);
               myMap.AddShape(pin);
      
               // Add the information to the resultsDiv html, including a link 
               // that recenters the map over the pin
               resHtml = resHtml + 
                         "<p><a href='javascript:myMap.SetCenter(new VELatLong(" +
                         latitude +
                         "," +
                         longitude +
                         "));'>";
               resHtml = resHtml + 
                         "#" + (p+1) +
                         ": " + place.Name +
                         " (" + precString +
                         ", " +
                         confString +
                         " confidence, " +
                         mcVal +
                         ")</a></p>";
            }
   
            // set the resultsDev html when we're done.
            document.getElementById("resultsDiv").innerHTML = resHtml;
         }
         
         function MatchCode(code)
         {
            if(code == VEMatchCode.None) {
               return "No match";
            }
   
            var codeDesc = "";   
            var cVal;
            
            cVal = code & VEMatchCode.Good;
            if(cVal > 0) {
              codeDesc += "Good ";
            }
   
            cVal = code & VEMatchCode.Ambiguous;
            if(cVal > 0) {
              codeDesc += "Ambiguous ";
            }
   
            cVal = code & VEMatchCode.UpHierarchy;
            if(cVal > 0) {
              codeDesc += "UpHierarchy ";
            }
   
            cVal = code & VEMatchCode.Modified;
            if(cVal > 0) {
              codeDesc += "Modified ";
            }
            
            return(codeDesc + "Match");
         }
                  
         function onGeocodeClick()
         {
            myMap.Clear();
            address = document.getElementById("txtWhere").value;
            StartGeocoding(address);
         }
      </script>
      <style type="text/css">
         .pinText
         { 
            position:relative; 
            top:-25px; 
            left:2px;
            width:30px;
            color:#ffffff; 
            text-align:center; 
           font: bold 12px Arial; 
         }
      </style>
   </head>
   <body onload="LoadMap()" onunload="UnloadMap()">
      <div style="font-family:Arial; font-size:10pt">
         Address: 
         <input id="txtWhere" type="text" style="width:255px" />&nbsp;
         <input type="button" value="Geocode" onclick="onGeocodeClick()" />
      </div><br />
   
      <div style="position:relative;width:400px;height:400px;" id="mapDiv"></div>
   
      <div id="resultsDiv" style="font-family:Arial;font-size:8pt;position:relative; top:-400px;left:425px;width:400px"></div>
   </body>
</html>
Show:
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