Introduction:

Yahoo Web Services are made available to developers through Yahoo's Developer Network; a variety of services are available but this article is specifically interested in using Yahoo's Geocoding Service. This service will return the closest matching address to a submitted physical address and will also return the addresses position in latitude and longitude. The terms and conditions for using the service are pretty simple; users are permitted to geocode up to 5,000 addresses per day for the very reasonable price of absolutely nothing.

This article will demonstrate the basics of submitting an address to the service, recovering and displaying the geocoded result, and will also demonstrate a simple approach to displaying the location as mapped using Yahoo maps. For more information regarding the program refer directly the Yahoo Developer Network website located at http://developer.yahoo.com/dotnet/.

On a limited basis, the service can be used to obtain and store latitude and longitude on all of the addresses contained in some sort of contact database or asset location database, or might be useful for storing waypoints in a GPS device. Naturally the service is based upon physical addresses so its use is limited to tagging physical addresses with a lat/long.

When visiting the site, take a look at the different programs available and take a look at some of the many services made available through Yahoo.

demostration-in-vb.net.gif

Figure 1: The demonstration application running

Displaying-the-coordinates-in-vb.net.gif

Figure 2: Displaying the coordinates in Yahoo Maps

Getting Started:

In order to get started, unzip the included project and open the solution in the Visual Studio 2005 environment. In the solution explorer, you should note these files:

Solution-Explorer-in-vb.net.gif

Figure 3: Solution Explorer

The Main Form (Form1.vb)

The main form is the only form contained in the application; all of the application specific code required to access the service, return the results of an address search, and to display those results as text or as a map are included in this class.

The code is pretty simple, if you'd care to open the code view up in the IDE you will see that the code file begins as follows:
Imports System.Xml

The only import is System.Xml.

Following the import, the class is defined and a default constructor added.

Public Class Form1

''' <summary>

''' Default Constructor

''' </summary>

''' <remarks></remarks>

Public Sub New()

' This call is required by the Windows Form Designer.

InitializeComponent()
End Sub

 Next up is the declaration of a structure used to contain the results returned from a request to geocode a physical address.

''' <summary>

''' Address Struct is used to contain

''' the elements of the geocoded address

''' returned from the Yahoo Map Service

''' </summary>

''' <remarks></remarks>

Public Structure Address

Public Street As String

Public City As String

Public State As String

Public Zip As String

Public Country As String

Public Latitude As String

Public Longitude As String

End Structure

' declare an address
 Private SearchAddress As Address

The next section of the code is used to request a search on an address; this request is submitted to Yahoo's service which returns the nearest matching address along with its latitude and longitude. The geocoded address returned from the service is stored in an Address.

''' <summary>

''' Call the Yahoo map service to geocode an address

''' and return that address to the caller

''' </summary>

''' <param name="street"></param>

''' <param name="city"></param>

''' <param name="state"></param>

''' <returns>A populated address</returns>

''' <remarks></remarks>

Private Function GetAddress(ByVal street As String, _ByVal city As String, _ByVal state AsString) As Address

Dim newAddress As New Address()

Dim reader As New XmlTextReader("http://local.yahooapis.com/MapsService/V1/geocode?appid=YahooDemo&street=" +
street + "&city=" + city + "&state=" + state)

' handle whitespace

reader.WhitespaceHandling = WhitespaceHandling.Significant

' get node values and populate address

While (reader.Read())

If reader.Name.ToString() = "Address" Then

newAddress.Street = reader.ReadString().ToString()

End If

If reader.Name.ToString() = "City" Then

newAddress.City = reader.ReadString().ToString()

End If

If reader.Name.ToString() = "State" Then

newAddress.State = reader.ReadString().ToString()

End If

If reader.Name.ToString() = "Zip" Then

newAddress.Zip = reader.ReadString().ToString()

End If

If reader.Name.ToString() = "Country" Then

newAddress.Country = reader.ReadString().ToString()

End If

If reader.Name.ToString() = "Latitude" Then

newAddress.Latitude = reader.ReadString().ToString()

End If

If reader.Name.ToString() = "Longitude" Then

newAddress.Longitude = reader.ReadString().ToString()

End If

End While

' return populated address

Return newAddress
 End Function
The find button click event handler starts a search for the user supplied address; the nearest match is displayed on the form's search results.

''' <summary>

''' Initiate a search for an address using the yahoo service; return

''' the geocoded results into an a new Address and the display

''' the values contained on that address using the textboxes

''' in the result section of the main form.

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub btnFind_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)Handles btnFind.Click

If (txtSearchCity.Text = String.Empty Or _txtSearchState.Text = String.Empty Or_txtSearchStreet.Text = String.Empty)

Then

MessageBox.Show("Complete all search terms prior to submitting a request.", "Invalid Request")

Return

End If

' setup a new address

SearchAddress = New Address()

Try

' populate the address

SearchAddress = GetAddress(txtSearchStreet.Text, _txtSearchCity.Text, _txtSearchState.Text)

Catch ex As Exception

MessageBox.Show(ex.Message, "Error")

End Try

' clear out the text from all of the result textboxes

CleanTextboxes()

' load the search results into the textboxes

Try

txtStreet.Text = SearchAddress.Street

txtCity.Text = SearchAddress.City

txtState.Text = SearchAddress.State

txtZip.Text = SearchAddress.Zip

txtCountry.Text = SearchAddress.Country

txtLatitude.Text = SearchAddress.Latitude

txtLongitude.Text = SearchAddress.Longitude

Catch ex As Exception

MessageBox.Show(ex.Message, "Error")

End Try

End Sub
The next bit of code is used to clear out all of the search results section text boxes.

''' <summary>

''' Clear the search results from the

''' textboxes

''' </summary>

''' <remarks></remarks>

Private Sub CleanTextboxes()

txtStreet.Text = String.Empty

txtCity.Text = String.Empty

txtState.Text = String.Empty

txtZip.Text = String.Empty

txtCountry.Text = String.Empty

txtLatitude.Text = String.Empty

txtLongitude.Text = String.Empty
 End Sub

 The next event handler exits the application if the user decides to shut down the program.

''' <summary>

''' Close the application upon user request

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub btnExit_Click(ByVal sender As System.Object, _ByVal e AsSystem.EventArgs)Handles btnExit.Click

' shut down application

Application.Exit()
 End Sub

 The last bit of code contained in the application is used open the Geocoded coordinates returned from the service into a running instance of Yahoo Maps. The approach here is simply to format a query string using the values returned from the service.

''' <summary>

''' Map the current location using the latitude and longitude

''' returned from the service

''' </summary>

''' <param name="sender"></param>

''' <param name="e"></param>

''' <remarks></remarks>

Private Sub btnMapLocation_Click(ByVal sender As System.Object, ByVal e AsSystem.EventArgs) Handles btnMapLocation.Click

Try

MessageBox.Show("Mapping Address: " + SearchAddress.Street.ToString(), _"Mapping Location")

Catch

MessageBox.Show("Invalid address", "Error")

Return

End Try

System.Diagnostics.Process.Start("iexplore.exe",_"http://maps.yahoo.com/#mvt=m&lat=" + SearchAddress.Latitude + _"&lon=" + SearchAddress.Longitude + "&mag=3&q1=" + SearchAddress.Latitude + _"%2C%20" + SearchAddress.Longitude)
 End Sub
Summary

This application was provided as an example of how one might take advantage of the Yahoo Address Geocoding service. This service, along with many others provided by Yahoo, is available at no cost to the developer. If one were required to geocode a collection of addresses yet lacked access to some of the available third party tools (such as the ESRI product line), this service could be invaluable. The service mentioned in this article is only a small part of the overall offering and I would encourage anyone interested in providing a low cost, web based mapping solution to investigate the Yahoo Developer's Network.