The terms of a contract can be evidenced by anything that shows a meeting of the minds, including the <i>actions</i> of the parties in implementing the contractual terms (so-called "course of performance").<p>There is no doubt that diagrams can be used in contracts and frequently are. Though a diagram would not stand alone, it would constitute strong or even conclusive evidence of the meaning of the prose part of a written contract (or the meaning of words exchanged by parties in the case of a verbal contract).<p>Bottom line: a meeting of the minds <i>always</i> has reference to some context and all of that context can be relevant to determining meaning - if a diagram helps show the context in which parties are agreeing to something, it can and should be used to add clarity to a contract.