In geometry, an arrangement of lines is the subdivision of the plane formed by a collection of lines. Bounds on the complexity of arrangements have been studied in discrete geometry, and computational geometers have found algorithms for the efficient construction of arrangements. Definition Intuitively, any finite set of lines in the plane cuts the plane into two-dimensional polygons (cells), one-dimensional line segments or rays, and zero-dimensional crossing points. This can be formalized mathematically by classifying the points of the plane according to which side of each line they are on. Each line separates the plane into two open half-planes, and each point of the plane has three possibilities per line: it can be in either one of these two half-planes, or it can be on the line itself. Two points can be considered to be equivalent if they have the same classification with respect to all of the lines. This is an equivalence relation, whose equivalence classes are subsets of equivalent points. These subsets subdivide the plane into shapes of the following three types: The cells or chambers of the arrangement are two-dimensional regions not part of any line. They form the interiors of bounded or unbounded convex polygons. If the plane is cut along all of the lines, these are the connected components of the points that remain uncut. The edges or panels of the arrangement are one-dimensional regions belonging to a single line. They are the open line segments and open infinite rays into which each line is partitioned by its crossing points with the other lines. That is, if one of the lines is cut by all the other lines, these are the connected components of its uncut points. The vertices of the arrangement are isolated points belonging to two or more lines, where those lines cross each other. The boundary of a cell is the system of edges that touch it, and the boundary of an edge is the set of vertices that touch it (one vertex for a ray and two for a line segment). The system of objects of all three types, linked by this boundary operator, form a cell complex covering the plane. Two arrangements are said to be isomorphic or combinatorially equivalent if there is a one-to-one boundary-preserving correspondence between the objects in their associated cell complexes. The same classification of points, and the same shapes of equivalence classes, can be used