Intellectual Highlighting of Remote Sensing Imagery for Better Image Map Design
ISBN 978-85-88783-11-9
Authors
1Murphy, C.E.
1DEPARTMENT OF CARTOGRAPHY, TECHNISCHE UNIVERSITÄT MÜNCHEN Email: christian.murphy@tum.de
Abstract
Image maps prove to be a useful cartographic medium, as the combination of remote sensing imagery with abstract cartographic symbolisation has become a frequently used visualisation option. Common image map design is dedicated solely to the graphic variation of the carto-graphic symbols. This work presents a new approach to image map design that visually high-lights important map objects of the remote sensing imagery in order to place these individual image objects into distinct levels of a visual hierarchy. The joint highlighting of important image objects as well as symbols improves the guiding of the user´s visual attention on the map and thereby aims to enhance the overall visual communication with image maps. In the first step of design, the cartographer should determine an intended hierarchy level for each object dependent on its intellectual importance. Objects of great relevance are sorted into higher levels and objects of minor relevance are retreated into lower visual levels. This concept enables that intellectually important objects are visualized with a stronger visual salience and therefore attract the user´s perception immediately. This work questions the default design of image maps by considering the design of the raster imagery to the same extent as the design of cartographic symbols. But, for raster imagery the freedom of graphical configuration is much more limited. The design of remote sensing imagery has to overcome two main problems. (1) Image objects (i.e. depicted buildings) can only be reasonably graphically modified to a degree that does not disguise their naturalistic reflection. And (2), only design operations can be applied that do not alter the image object´s spatial footprint. Every spatial offset from the object´s original location on the pixel image will make the entire image illegible and highly confusing to the user. Based on image processing, design strategies are introduced that respect the limitations in the freedom of design for remote sensing imagery. The design strategies utilise pre-attentive vari-ables that increase the saliency of important image objects and decrease the saliency of image context information, while maintaining the object´s naturalistic reflection as well as its image context. The intellectual ordering of various objects of remote sensing imagery into an intend-ed visual hierarchy of image maps is verified in examples of use.