public bool QueryDiagramEdgeElement {get; set;}

{
  // Get the diagram elements whose extent intersects the active map extent
  static void GetDiagramElements(MapView mapView, NetworkDiagram networkDiagram)
  {
    // Create a DiagramElementQueryByExtent to retrieve diagram element junctions whose extent
    // intersects the active map extent

    DiagramElementQueryByExtent elementQuery = new DiagramElementQueryByExtent();
    elementQuery.ExtentOfInterest = MapView.Active.Extent;
    elementQuery.AddContents = false;
    elementQuery.QueryDiagramJunctionElement = true;
    elementQuery.QueryDiagramEdgeElement = false;
    elementQuery.QueryDiagramContainerElement = false;

    // Use this DiagramElementQueryByExtent as an argument to the QueryDiagramElements method
    DiagramElementQueryResult result = networkDiagram.QueryDiagramElements(elementQuery);

    // Get the container, junction, edge elements. 

    IReadOnlyList<DiagramContainerElement> containerElements = result.DiagramContainerElements;

    // In this case result.DiagramJunctionElements and result.DiagramEdgeElements will be empty
    // because elementQuery.QueryDiagramEdgeElement and elementQuery.QueryDiagramContainerElement are set to 'false'
    IReadOnlyList<DiagramJunctionElement> junctionElements = result.DiagramJunctionElements;

    IReadOnlyList<DiagramEdgeElement> edgeElements = result.DiagramEdgeElements;
  }
}

{
  // Change the layout of a network diagram by querying for all the diagram elements, editing their shapes,
  static void ChangeDiagramLayout(DiagramManager diagramManager, string diagramName)
  {
    // Retrieve a diagram
    using (NetworkDiagram diagramTest = diagramManager.GetNetworkDiagram(diagramName))
    {
      // Create a DiagramElementQueryByElementTypes query object to get the diagram elements we want to work with
      DiagramElementQueryByElementTypes query = new DiagramElementQueryByElementTypes();
      query.QueryDiagramJunctionElement = true;
      query.QueryDiagramEdgeElement = true;
      query.QueryDiagramContainerElement = true;

      // Retrieve those diagram elements
      DiagramElementQueryResult elements = diagramTest.QueryDiagramElements(query);

      // Create a NetworkDiagramSubset object to edit this set of diagram elements
      NetworkDiagramSubset subset = new NetworkDiagramSubset();
      subset.DiagramJunctionElements = elements.DiagramJunctionElements;
      subset.DiagramEdgeElements = elements.DiagramEdgeElements;
      subset.DiagramContainerElements = elements.DiagramContainerElements;

      // Save the new layout of the diagram elements
      diagramTest.SaveLayout(subset, true);
    }
  }
}