Let be a commutative, indecomposable ring with identity and let be a locally finite partially ordered set. Let denote the finitary incidence algebra of over . In this case, the finitary incidence algebra exactly coincides with the incidence space. We will give an explicit criterion for when local automorphisms of are actually -algebra automorphisms. We will also show that cases which do not meet that criterion may have nonsurjective local automorphisms- in particular, those maps are not -algebra automorphisms, showing a strict inclusion of the collection of -algebra automorphisms inside the collection of local automorphisms. In fact, the existence of local automorphisms which fail to be -algebra automorphisms will depend on the chosen model of set theory and will require the existence of measurable cardinals. We will discuss local automorphisms of cartesian products as a special case in preparation of the general result. Finally, we will explore the automorphisms and local automorphisms of the where is a free -module and is no longer necessarily indecomposable.