Area preserving cartographic line generalization 84 KiG 2009, 11 Area Preserving Cartographic Line Generalization Draen TUTIÆ, Miljenko LAPAINE University of Zagreb, Faculty of Geodesy, Zagreb, Croatia e-mail: dtutic@geof.hr, mlapaine@geof.hr Abstract: Cartographic line generalization is a gen- eralization with the primary purpose of obtaining a line shape suitable for representation on maps at smaller scales than the scale of the given lines. Ex- isting literature also differentiates model generaliza- tion and geographic generalization, each with a pri- mary purpose. A new algorithm for cartographic gen- eralization with distinct property of area preservation is described in this paper. The algorithm yields gen- eralized lines with a subset of points from given lines together with new points. For that reason, it can be considered partially as simplification and partially as a smoothing process. Area preservation is not often considered in research on cartographic line general- ization. Such research mostly stresses the importance of the line shape. A detailed description of the new algorithm is given in this paper, as well as the results of the application on coastlines. A comparison with manual line generalization, the Douglas-Peucker sim- plification algorithm, the Boyle smoothing algorithm and the combination of the latter two is also given. The tests show the new algorithm yields satisfactory results for cartographic line generalization. The prop- erty of area preservation is especially suitable for application in GIS when attributes are represented or analysed in regard to object areas. Key words: cartographic generalization, lines, area preservation 1 Motivation Results of automatic vectorisation of linear features from raster maps can contain irregularities which cause unnecessary zigzags in vector lines (Fig. 1). A simple solution of the problem described is to de- lete segments shorter than a given length and the angle to the one neighbouring segment is larger than 180° and the angle to the other neighbouring segment is smaller than 180°, measured on the same side. Based on that problem, the idea for applying such a method or a similar one to a more general task of carto- graphic line generalization emerged. 2 Introduction Cartographic line generalization is one of the major research areas in the more general area of cartographic generalization. The number of existing papers for the area of cartographic line generalization is large, especially since line generalization is also performed with comput- ers. Valuable bibliographic resources for cartographic generalization can be found at (URL1, URL2). There exist a number of methods for automatic line generalization, each using a different approach and meth- odology. Cartographic theory differentiates sub-process- es in line generalization, such as filtering, simplification, smoothing, etc. An overview of more important algorithms Preliminary Paper Received: 15-05-2009 Accepted: 15-06-2009