How to create AOIs and bookmarks

private void AddSpatialBookMark(IApplication application)
{
    IMapDocument mapDoc = application.Document as IMapDocument;
    IMap map = mapDoc.ActiveView.FocusMap;
    IActiveView activeView = map as IActiveView;

    // Create a new bookmark and set its location to the focus map's current extent.
    IAOIBookmark areaOfInterest = new AOIBookmarkClass();
    areaOfInterest.Location = activeView.Extent;

    // Give the bookmark a name.
    areaOfInterest.Name = "Area of Interest Bookmark";

    // Add the bookmark to the map's bookmark collection. This adds the bookmark 
    // to the Bookmarks menu, which is accessible from the View menu.
    IMapBookmarks mapBookmarks = map as IMapBookmarks;
    mapBookmarks.AddBookmark(areaOfInterest);
}

Private Sub AddSpatialBookMark(ByVal application As IApplication)
    
    Dim mapDoc As IMapDocument = TryCast(application.Document, IMapDocument)
    Dim map As IMap = mapDoc.ActiveView.FocusMap
    Dim activeView As IActiveView = TryCast(map, IActiveView)
    
    ' Create a new bookmark and set its location to the focus map's current extent.
    Dim areaOfInterest As IAOIBookmark = New AOIBookmarkClass()
    areaOfInterest.Location = activeView.Extent
    
    ' Give the bookmark a name.
    areaOfInterest.Name = "Area of Interest Bookmark"
    
    ' Add the bookmark to the map's bookmark collection. This adds
    ' the bookmark to the Bookmarks menu accessible from the View menu.
    Dim mapBookmarks As IMapBookmarks = TryCast(map, IMapBookmarks)
    mapBookmarks.AddBookmark(areaOfInterest)
    
End Sub

private void ZoomToBookmark(IApplication application, IMxDocument mxDocument)
{
    IDocument document = application.Document;
    IMapDocument mapDoc = document as IMapDocument;
    IActiveView activeView = mapDoc.ActiveView;
    IMap map = activeView.FocusMap;

    // Access the Map object through its IMapBookmarks interface.
    IMapBookmarks mapBookmarks = map as IMapBookmarks;

    // Get an enumeration of bookmarks.
    IEnumSpatialBookmark enumSpatialBookmark = mapBookmarks.Bookmarks;
    enumSpatialBookmark.Reset();
    ISpatialBookmark spatialBookmark = enumSpatialBookmark.Next();

    while (spatialBookmark != null)
    {
        if (spatialBookmark.Name == "Area of Interest Bookmark")
        {
            // Zoom to spatialBookmark.
            spatialBookmark.ZoomTo(map);
            activeView.Refresh();
            return ;
        }
        spatialBookmark = enumSpatialBookmark.Next();
    }
}

Private Sub ZoomToBookmark(ByVal application As IApplication, ByVal mxDocument As IMxDocument)
    
    Dim document As IDocument = application.Document
    Dim mapDoc As IMapDocument = TryCast(document, IMapDocument)
    Dim activeView As IActiveView = mapDoc.ActiveView
    Dim map As IMap = activeView.FocusMap
    
    ' Access the Map object through its IMapBookmarks interface.
    Dim mapBookmarks As IMapBookmarks = TryCast(map, IMapBookmarks)
    
    ' Get an enumeration of bookmarks.
    Dim enumSpatialBookmark As IEnumSpatialBookmark = mapBookmarks.Bookmarks
    enumSpatialBookmark.Reset()
    Dim spatialBookmark As ISpatialBookmark = enumSpatialBookmark.Next()
    
    While (spatialBookmark IsNot Nothing)
        
        If (spatialBookmark.Name Is "Area of Interest Bookmark") Then
            
            ' Zoom to spatialBookmark.
            spatialBookmark.ZoomTo(map)
            activeView.Refresh()
            Return
        End If
        
        spatialBookmark = enumSpatialBookmark.Next()
        
    End While
    
End Sub