One of the most recurring themes in many computer applications such as
the hidden-line problem of graphics, scene analysis, automated
cartography and image processing is the notion of visibility.  This
report addresses the visibility between two edges of a configuration of
adjacent rectangles.  This problem stems from work done in the ray
guarding of configurations of adjacent rectangles.  In ray guarding
these rectangles, it is necessary to be able to find a straight line
through a set of adjacencies in a group of adjacent rectangles.  If
the adjacent rectangles are visualised as a simple polygon, whose
boundary is the boundary of the rectangles excluding the adjacencies
between the rectangles, then the problem is one of finding a straight
line, from one edge of the polygon to another, that is completely
contained within the polygon.  A linear running time, and thus optimal
algorithm is presented to determine the partial edge visibility in
such a polygon.