public class GeoJsonFileDataAdapter :
    FileDataAdapterBase

Public Class GeoJsonFileDataAdapter
    Inherits FileDataAdapterBase

private void Form1_Load(object sender, EventArgs e) {

    ImageLayer imageLayer = new ImageLayer {
        DataProvider = new BingMapDataProvider { BingKey = "Your_BingKey_here", Kind = BingMapKind.Road }
    };
    mapControl1.Layers.Add(imageLayer);

    VectorItemsLayer vectorLayer = new VectorItemsLayer();
    mapControl1.Layers.Add(vectorLayer);

    GeoJsonFileDataAdapter dataAdapter = new GeoJsonFileDataAdapter();
    dataAdapter.FileUri = new Uri(GetRelativePath("Data\\subway-entrances.geojson"), UriKind.RelativeOrAbsolute);
    vectorLayer.Data = dataAdapter;

    // Use the ItemsLoaded event to customize items the adapter generates.
    dataAdapter.ItemsLoaded += OnDataAdapterItemsLoaded;
    // You can call the MapControl.ZoomToFitLayerItems method in the DataLoaded event handler
    // to zoom the map so that it displays all vector items.
    vectorLayer.DataLoaded += OnVectorLayerDataLoaded;
}

private void OnDataAdapterItemsLoaded(object sender, ItemsLoadedEventArgs e) {
    foreach (MapDot item in e.Items) {
        item.Fill = Color.Red;
        item.Size = 8;                
    }
}

private void OnVectorLayerDataLoaded(object sender, DataLoadedEventArgs e) {
    mapControl1.ZoomToFitLayerItems(new List<LayerBase> { (VectorItemsLayer)mapControl1.Layers[1] });
}

public static string GetRelativePath(string name) {

    DirectoryInfo dir = new DirectoryInfo(Application.StartupPath);
    while (dir != null) {
        string filePath = Path.Combine(dir.FullName, name);
        if (File.Exists(filePath))
            return filePath;
        dir = Directory.GetParent(dir.FullName);
    }
    return string.Empty;
}

Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs)
    Dim imageLayer As ImageLayer = New ImageLayer With {
        .DataProvider = New BingMapDataProvider With {
            .BingKey = "Your_BingKey_here",
            .Kind = BingMapKind.Road
        }
    }
    mapControl1.Layers.Add(imageLayer)
    Dim vectorLayer As VectorItemsLayer = New VectorItemsLayer()
    mapControl1.Layers.Add(vectorLayer)
    Dim dataAdapter As GeoJsonFileDataAdapter = New GeoJsonFileDataAdapter()
    dataAdapter.FileUri = New Uri(GetRelativePath("Data\subway-entrances.geojson"), UriKind.RelativeOrAbsolute)
    vectorLayer.Data = dataAdapter

    ' Use the ItemsLoaded event to customize items the adapter generates.
    dataAdapter.ItemsLoaded += AddressOf OnDataAdapterItemsLoaded
    ' You can call the MapControl.ZoomToFitLayerItems method in the DataLoaded event handler
    ' to zoom the map so that it displays all vector items.
    vectorLayer.DataLoaded += AddressOf OnVectorLayerDataLoaded
End Sub

Private Sub OnDataAdapterItemsLoaded(ByVal sender As Object, ByVal e As ItemsLoadedEventArgs)
    For Each item As MapDot In e.Items
        item.Fill = Color.Red
        item.Size = 8
    Next
End Sub

Private Sub OnVectorLayerDataLoaded(ByVal sender As Object, ByVal e As DataLoadedEventArgs)
    mapControl1.ZoomToFitLayerItems(New List(Of LayerBase) From {
        CType(mapControl1.Layers(1), VectorItemsLayer)
    })
End Sub

Public Shared Function GetRelativePath(ByVal name As String) As String
    Dim dir As DirectoryInfo = New DirectoryInfo(Application.StartupPath)

    While dir IsNot Nothing
        Dim filePath As String = Path.Combine(dir.FullName, name)
        If File.Exists(filePath) Then Return filePath
        dir = Directory.GetParent(dir.FullName)
    End While

    Return String.Empty
End Function