This code will show you how you can search within a specific radius of an area using a zip code.

This code snip provides a way of implementing a radius search within your application. One of the first things you need to do is obtain a database of zipcodes with latitude and longitude coordinates. You can do a search on Google and find databases containing the information for under $100.

Dim HighLatitude 
Dim LowLatitude 
Dim LowLongitude 
Dim HighLongitude 

Function GetDistance(Lat1, Long1, Lat2, Long2, Unit)
      Dim x
      x = (sin(DegToRads(Lat1)) * sin(DegToRads(Lat2)) + cos(DegToRads(Lat1)) * _
          cos(DegToRads(Lat2)) * cos(abs((DegToRads(long2))-(DegToRads(long1)))))
      ' Get Acos(x)
      x = atn((sqr(1-x^2))/x)
      ' Get distance in kilometers
      GetDistance = 1.852 * 60.0 * ((x/pi)*180)
      ' Convert units if necessary
      Select Case ucase(Unit)
         Case "M"      
            GetDistance = GetDistance / 1.609344
         Case "N"
            GetDistance = GetDistance / 1.852
      End Select
End Function
'_________________________________
Sub SetRadius(iRadius, iZip)
	' THIS VARIABLE SETS THE RADIUS IN MILES

	Dim rs, SQLQ, iStartlat, iStartlong, LatRange, LongRange
	SQLQ = "SELECT LATITUDE, LONGITUDE FROM ZIPCODES WHERE ZIPCODE = '" & iZip & "'"
	Set rs = DBConn.Execute(SQLQ)
	If Not rs.EOF Then
		iStartlat = rs(0)
		iStartlong = rs(1)
	End If
	rs.Close
	Set rs = Nothing
	LatRange = iRadius / ((6076 / 5280) * 60)
	LongRange = iRadius / (((cos(cdbl(iStartLat * 3.141592653589 / 180)) * 6076.) / 5280.) * 60)
	
	LowLatitude = iStartlat - LatRange
	HighLatitude = iStartlat + LatRange
	LowLongitude = iStartlong - LongRange
	HighLongitude = iStartlong + LongRange
End Sub
'_________________________________________________________
'condition for building SQL String:

If Request("radius") <> "0" Then
		Call SetRadius(CLng(Request("radius")), Request("zipcode"))
		SQLQ = SQLQ & JoinWord & " Company_Postal_Code IN(SELECT ZIPCODE " & _
                                    "FROM ZIPCODES WHERE LATITUDE <= " & HighLatitude & " AND LATITUDE >= " & LowLatitude & _
			" AND LONGITUDE >= " & LowLongitude & _
			" AND LONGITUDE <= " & HighLongitude & ")"
		JoinWord = " AND "
End If