what is the difference between a vintige and a dio???
I think you mean a vignette and a dio. A vignette is usually one or two figures and some ground work, that is about all. The focal piece is the figure(s). A diorama is usually a vehicle or collection of vehicles with groundwork, buildings, figures etc. A diorama usually tries to show an event or a story. The focus is not any one vehicle or figure, but the story presented. The real question is when does a vignette become a diorama? Hhmm!!
What Gino said. The number of figures can vary by the organization doing the judging. One figure is never considered a vignette, though only one figure maight be represented in a diorama. Figure artists may have 5-7 figures in a tight formation and it would still be a vignette. Pretty much when you add vehicles or significant architectural structures to the scene it becomes a diorama.