BUFFERING IN GEOGRAPHIC INFORMATION SYSTEM CHHABI RAM BARAL* BACKGROUND Buffering in general refers the creation of a zone of a specified width around a point or a line or a polygon area. The buffer operation takes two parameters: a buffer distance and the object around which the buffer is to be created but spatial data usually consist of different types of objects. Object types include points, lines and polygons. The idea of providing primitives for basic buffer operations started soon after the inception of spatial databases themselves. Working on atomic units of points was soon found to be not a very scalable option. The search for a more scalable and computationally efficient technique led to the introduction of buffer primitives. DEFINITION One of the most important transformations available to the GIS user is the buffer operation. Given any set of objects, which may include points, lines, or areas, a buffer operation builds a new object or objects by identifying all areas that are within a certain specified distance of the original objects. In case of Geographical Information Systems, the units of buffering are points, lines, and polygons. Buffer operation refers the creation of a zone of a specified width around a point, a line or a polygon area. It is also referred to as a zone of specified distance around coverage features. There are two types of buffers: constant width buffers and variable width buffers. Both types can be generated for a set of coverage features based on each features attribute values. These zones or buffers can be used in queries to determine which entities occur either within or outside the defined buffer zone. Analogous to buffering in raster GIS is distance analysis. In practical situations, one needs to buffer multiple regions (points, lines and polygons) simultaneously. This gives rise to the idea of buffer allocation and replacement. Data movement happens by making use of primitive buffer operations such as point buffer operation, line buffer operation and polygon buffer operations. Buffer management involves the process of allocation of buffers and replacement of buffers when not needed. Several allocation policies and replacement policies that have been used in the context of memory buffers in computer science are directly applicable here. CLASSIFICATION OF BUFFERING In GIS, we can classify buffer primitives as point buffering operations, line buffering operations, and polygon buffering operations. Point Buffering: A point is the basic unit of resolution in any GIS system. Buffering point data involves the creation of a circular polygon about the point of interest. The radius of this circular polygon is called the buffer distance. In this scheme the buffer distance or the radius of the circle could be fixed for all points in a layer or the user could specify it. If multiple points in the same layer are *Mr. Baral is Teaching Assistance of Department of Geography,Patan Multiple Campus Tribhuvan University, Nepal.