Geocoding a Physical Address using Yahoo Web Services and Visual Basic

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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 address' 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 to the Yahoo Developer Network website located here.

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.

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:

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 As String) 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 a new Address and then 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 As System.EventArgs) Handles btnExit.Click

    ' shut down application
    Application.Exit()

End Sub

The last bit of code contained in the application is used to 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 As System.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.