The MAP (Metaphysical Autology Principle) is a very general philosophical principle of the CTMU.
In essence, it states that reality is self-contained, and there is nothing external to reality. In essence, if something existed external to reality, it would be existing outside of reality, which is logically impossible. Hence, there is nothing external to reality with respect to the laws of existence. Also, because reality is self contained; it must contain in itself the means for its own explanation. That is to say that every part of reality must be describable in terms of some other part of reality. For example, if reality consisted of three objects A, B and C then A may be defined in terms of B which can be defined in terms of C which can be defined in terms of A. In this way reality's definition of aspects of itself is Closed.
The following link graphically demonstrates the principle of Closure; http://megafoundation.org/CTMU/images/MAP.jpg
Although to many people this principle might seem utterly trivial, Langan argues that in fact it is not, as scientists tend to violate it often, inadvertently or otherwise. For example, M-theorists and Superstring theorists often propose a higher-dimensional space (i.e. an 11-dimensional spacetime). However, the postulation of this higher-dimensional space cannot really be external to reality, for if it were, there would be no means to identify it or theorize about it. Hence, if 11-dimensional (26-dimensional, n-dimensional, etc.) spacetime exists, it must be internal to reality.
Another example is the recent advent in science of the popularization of Everett's "Many Worlds" interpretation of quantum theory. Langan objects to the Many Worlds interpretation, arguing that if there were these infinitely many parallel quantum realities they would have to be connected to some one fundamental reality, or else there would be no connection between their existential laws, and thus it would be impossible to identify them or scientifically verify their existence.
Thus, although prima facie MAP may seem trivial, Langan argues that it is in fact far from trivial, and theorists overlooking it in their explanations often leads to grave paradoxes and logical inconsistencies.
All relations, mappings and functions relevant to reality in a generalized effective sense, whether descriptive, definitive, compositional, attributive, nomological or interpretative, are generated, defined and parameterized within reality itself. In other words, reality comprises a "closed descriptive manifold" from which no essential predicate is omitted, and which thus contains no critical gap that leaves any essential aspect of structure unexplained. Any such gap would imply non-closure.