I think that all ASP.NET MVC concepts do not map to ASP.NET forms, because they are two different paradigms for building a web application.
In WebForms, people mostly deal with controls and set their properties; they do not need to pass data for viewing as such. However, if they need it, they use Page.Items or HttpContext.Current.Items or create the page properties that they access in views.
There is no direct equivalent to ViewData or ViewModel in WebForms, which is used in practice. Page.Items are the closest thing.
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