Design and applications of sector buffers for point feature
点要素扇形缓冲区的设计与应用

Traditionally,buffer zones of point features are circles with multiple radii. This means that same effect is used within the same radius around a point feature. In fact,a region affected by a point feature is possibly a sector buffer zone,not a circle,due to affecting factors such as wind direction,mountain range,ocean,transportation and so forth. The objective of this study is to enrich the theory and method of buffer zoning in GIS spatial analysis so as to meet the need of analyzing sector buffer zone for point features. Sector buffer zones are discussed with respect to its definition,data structure,fundamentals,algorithms and possible applications. To analyze point features with sector buffer zones,we developed a module using Visual Basic.NET and ArcObjects within ARC\INFO 9.3. After creating a polygon layer,iteratively,the layer field values are read iteratively,and the coordinates of the arc endpoints and chord length are calculated. Then the arc and the two edges of the sector were added,respectively,into the instance defined by an ISegmentCollection which then is assigned to a feature shape. If necessary,the overlaing polygons are handled. Sector buffer wizards with five forms were developed to select different methods and parameters conveniently according to different demands. The wizard provides more choices including the selection of features,radii,central angles,and initial angles. This module can append to ArcMap or ArcToolbox to use it conveniently,automatically,and dynamically. To validate the practicability,applicability,and effectiveness of sector buffer zones,two examples are used for demonstration. One uses sector buffer zones of video cameras distributed on the crossing roads in Kaifeng City,Henan Province,China. The other example analyzes the relationship between rural household income and rural migrant workers in Huangzhuang Village in Zhenping County,Henan Province,China,using the sector buffer zone method. A circle buffer zone is a special case of a sector buffer zone when the central angle of the sector is equal to 360°. Sector buffer zone is an expansion of the circle buffer zone. Results indicate that sector buffer zone,compared to circle buffer zone,has more information and regularities. It is very convenient for the analysis of point feature to reach more credible conclusions and to make decisions for administrators more accurately. In the future,more methods for drawing buffer zones with respect to point features,polyline features,and polygon features will be studied to make buffer system more robust and more perfect so as to meet the need of spatial analysis.