Question

I have a VBA macro that uses Microsoft MapPoint to calculate the distance between two locations for each record in my spreadsheet. I have about 120,000 records to process. The program runs smoothly for about 10,000 iterations then returns a Type Mismatch error where I define the MapPoint locations in my error handler. At which point, I select ‘Debug’ and then resume execution without editing any code, and it will run successfully for another 10,000 or so records before the same thing happens again.

I’ve checked my data, and I can’t see why there would be a type mismatch, or for that matter why the code would choke on a record one time, and then, without resetting anything, handle the same record upon resuming. Any idea why this would happen?

For reference,
– column M contains locations of the form “X County, ST”
– column AN contains a separate location as ZIP
– column G contains the same location data as AN but in the form “X County, ST”

Sub distance_from_res()
Dim oApp As MapPoint.Application
Dim k As Long  
Dim count As Long 
Dim errors As Long 

k = 0
count = Sheets("i1_20041").Range("A2", Sheets("i1_20041").Range("A2").End(xlDown)).count
errors = 0

  Set oApp = CreateObject("MapPoint.Application.NA.11")
  oApp.Visible = False
  Set objMap = oApp.NewMap
  Dim objRes As MapPoint.Location
  Dim objFish As MapPoint.Location

'Error executes code at 'LocError' and then returns to point of error.
  On Error GoTo LocError
  Do While k < count
    If Sheets("i1_20041").Range("M2").Offset(k, 0) <> "" Then
        'Sets MapPoint locations as [County],[State] from Excel sheet columns "INT_CNTY_ST" and "ZIP".
          Set objRes = objMap.FindResults(Sheets("i1_20041").Range("AN2").Offset(k, 0)).Item(1)
          Set objFish = objMap.FindResults(Sheets("i1_20041").Range("M2").Offset(k, 0)).Item(1)
        'Calculates distance between two locations and prints it in appropriate cell in Column AO.
          Sheets("i1_20041").Range("AO2").Offset(k, 0) = objRes.DistanceTo(objFish)
    Else
        errors = errors + 1
    End If
      k = k + 1
  Loop
 'Displays appropriate message at termination of program.
  If errors = 0 Then
    MsgBox ("All distance calculations were successful!")
  Else
    MsgBox ("Complete! Distance could not be calculated for " & errors & " of " & count & " records.")
  End If

Exit Sub

LocError:
    If Sheets("i1_20041").Range("G2").Offset(k, 0) = "" Then
        errors = errors + 1
    Else
        'THIS IS WHERE THE ERROR OCCURS!
          Set objRes = objMap.FindResults(Sheets("i1_20041").Range("G2").Offset(k, 0)).Item(1)
          Set objFish = objMap.FindResults(Sheets("i1_20041").Range("M2").Offset(k, 0)).Item(1)
        'Calculates distance between two locations and prints it in appropriate cell in Column AO.
          Sheets("i1_20041").Range("AO2").Offset(k, 0) = objRes.DistanceTo(objFish)
    End If
      k = k + 1
    Resume


End Sub

UPDATE:
I incorporated most of the suggestions from @winwaed and @Mike D, and my code is now more accurate and doesn’t choke on errors. However, the old problem reared its head in a new form. Now, after around 10,000 iterations, the code continues but prints the distance of the ~10,000th record for every record afterwards. I can restart the code at the trouble point, and it will find the distances normally for those records. Why would this happen? I’ve posted my updated code below.

Sub distance_from_res()

Dim oApp As MapPoint.Application
Dim k As Long 
Dim rc As Long 
Dim errors As Long

Dim dist As Double
Dim zipRes As Range
Dim coRes As Range
Dim coInt As Range
Dim distR As Range

Set zipRes = Sheets("Sheet1").Range("C2")
Set coRes = Sheets("Sheet1").Range("B2")
Set coInt = Sheets("Sheet1").Range("E2")
Set distR = Sheets("Sheet1").Range("G2")

k = 0
rc = Sheets("Sheet1").Range("F2", Sheets("Sheet1").Range("F2").End(xlDown)).Count
errors = 0

'Start MapPoint application.
Set oApp = CreateObject("MapPoint.Application.NA.11")
oApp.Visible = False
Set objMap = oApp.NewMap
Dim objResultsRes As MapPoint.FindResults
Dim objResultsInt As MapPoint.FindResults
Dim objRes As MapPoint.Location
Dim objInt As MapPoint.Location

Do While k < rc
    'Check results for Res Zip Code.  If good, set first result to objRes.  If not, check results for Res County,ST.  If good, set first result to objRes.  Else, set objRes to Nothing.
    Set objResultsRes = objMap.FindResults(zipRes.Offset(k, 0))
    If objResultsRes.ResultsQuality = geoFirstResultGood Then
        Set objRes = objResultsRes.Item(1)
    Else
        Set objResultsRes = Nothing
        Set objResultsRes = objMap.FindResults(coRes.Offset(k, 0))
        If objResultsRes.ResultsQuality = geoFirstResultGood Then
            Set objRes = objResultsRes.Item(1)
        Else
            If objResultsRes.ResultsQuality = geoAmbiguousResults Then
                Set objRes = objResultsRes.Item(1)
            Else
                Set objRes = Nothing
            End If
        End If
    End If

    Set objResultsInt = objMap.FindResults(coInt.Offset(k, 0))
    If objResultsInt.ResultsQuality = geoFirstResultGood Then
        Set objInt = objResultsInt.Item(1)
    Else
        If objResultsInt.ResultsQuality = geoAmbiguousResults Then
            Set objInt = objResultsInt.Item(1)
        Else
            Set objInt = Nothing
        End If
    End If

    On Error GoTo ErrDist
    distR.Offset(k, 0) = objRes.DistanceTo(objInt)

    k = k + 1
Loop

Exit Sub


ErrDist:
    errors = errors + 1
    Resume Next

End Sub

Answer 1

MikeD is right with your dangerous FindResults() calls. However, there is a better way to check the results. The “FindResults collection” isn’t a pure collection but includes an extra properties called “ResultsQuality”. Docs are here:

http://msdn.microsoft.com/en-us/library/aa493061.aspx

Resultsquality returns a GeoFindResultsQuality enumeration. You want to check for the values geoAllResultsGood and geFirstResultGood. All other results should give an error of some result. Note that your existing code would work find with (for example) Ambiguous Results, even though it is unlikely the first result is the correct one. Also it might match on State or Zipcode (because that is the best it can find) whcih give you an erroneous result. Using ResultsQuality, you can detect this.

I would still check the value of Count as an additional check.

Note that your code is calculating straight line (Great Circle) distances. As such the bottleneck will be the geocoding (FindResults). If you are using the same locations a lot, then a caching mechanism could greatly speed things up.
If you want to calculate driving distances, then there are a number of products on the market for this (yes I wrote two of them!).