Inset Mapper: a tool for scale selection and inset placing configuration of multiple insets in island cartography

Abstract

Cartographic design is a process of scale selection, symbolization and placement of geographical information. In Island Cartography scientists are faced with a unique and special cartographic problem, that of land discontinuity, which arises when scientists want to visualize islands regions with multiple islands of significantly different size. The most efficient cartographic solution, in this situation is the creation of an inset map. Cartographers typically use their judgment to determine the need of an inset. They visually inspect the map and subjectively identify the limits of areas which are “too crowded”, “too small”, ‘too dense” or “too isolated”. Inset maps should be created by cartographers following some specific cartographic rules for position and scale selection. Inset map placement is also influenced by the cartographer’s artistic view. The key factor for insetting in Island Cartography is the “complexity of land discontinuity” comprised of a number of islands that vary in size and shape creating a complex area surrounded by sea. It is very common for small and big size islands to coexist, thus rendering representation at the same scale problematic. The scale of the main map often causes small size islands not to be clearly visible by the map reader or not to be clearly drawn. Inset Mapper is a software tool for automated place and scale selection for inset maps that overcomes these procedure difficulties. IM is developed in MATLAB, along with other pertinent cartographic functionalities. This software tool attempts to emulate the steps a cartographer takes when deciding where to place and in which scale within a map to inset. To meet these requirements, IM employs some new strategies of cartographic representation for the inset placement procedure, and for scale selection, in multiple inset maps. Inset Mapper lays out the main and inset maps in four steps. At the first step the user selects the area of the map to inset, and chooses where IM to search for insets, either the quadrant the above selected area belongs into or the entire main map area. In the second step IM selects the appropriate scale of the inset map for the selected area. The choice of the parent scale determines both the size and place of the inset maps. in the third step IM renders colored boxed areas designating the proposed map placements within the main map. These preferred inset places depend on the number of natural groups of proposed insets. Finally, the user selects the preferred inset placement from those proposed by IM. This process can be repeated, so the cartographer is able to assign more than one insets in the same map. This paper discusses the theory and application of the algorithms used to choose a map scale, detect areas suitable for the placement of inset maps and delineate the best inset. These algorithms apply a combination of cartographic principles and analysis of the represented data. IM employs data clustering algorithms to select and to propose the best inset place, from a large number of contiguous insets that can be placed on map. Data clustering is employed to identify natural groups of proposed inset places in the main map. At the end the inset is placed into the right location within the map using a number of rules and membership grades for each cluster group. Finally a case study is presented, with Inset Mapper results for multiple insets on three different maps selected to cover local, regional and continental geographic scales.