Design guidelines for map mashups visualizing point data

Map mashups consisting of a background map and overlaid thematic information from different sources are today common map products, and they are used for different purposes ranging from applications for domain experts to maps created by ordinary people. Despite this prevalence the efficient communication and use of map mashups is not widely studied, and cartographic textbooks do not give guidelines for designing them. This dissertation is the first step to fill this gap by investigating the visualization of map mashups consisting of a back-ground map and point symbols overlaid on top of it. Three design issues that are relevant for map mashups are studied: 1) the design of pictographic symbols, 2) the management of over-crowding of the symbols, and 3) the visual highlighting of the symbols in an interactive application. The design issues are studied by a combination of qualitative and quantitative research methods, and the aim was to produce theoretical knowledge from the three design issues and to use this knowledge for formulating practical guidelines for achieving good map mashup products. The results concerning the pictographic map symbols indicate that a set of universal qualities define the success of all pictographic symbols. This dissertation provides ten qualities that the symbols should possess as well as practical guidelines for achieving the qualities. In addition to maximizing the universal qualities, the users of the symbols should be taken into account in the design, because the cultural background of the users affects the comprehension andvaluation of the symbols. This dissertation provides a model that identifies the tracks via which the cultural background affects the comprehension and valuation of the symbols. These tracks are based on differences in code systems, conceptual models and aesthetic judgments. Also, guidelines for symbols for intercultural use are proposed. The results concerning the over-crowding of symbols indicate that symbol occlusion decreases the efficiency of the map, and that the design and visual variables of the symbols affect the occlusion tolerance. Therefore, symbolization is a valid method to manage the effect of overcrowding. However, symbolization is a usable method only to a certain degree, and other methods may be more suitable for some situations. The suitability of the methods for a specific map mashup depends from a set of requirements that are set by the purpose of use of the map. This dissertation provides a table that can be used to choose a suitable overcrowding management method for a specific map mashup. The results concerning the highlighting of symbols indicate that the most successful strategy for highlighting is to increase the saliency difference between the highlighted and non-highlighted symbols.