ADDING METADATA TO MAPS AND STYLED LAYERS TO IMPROVE MAP EFFICIENCY

Transcription

1 ADDING METADATA TO MAPS AND STYLED LAYERS TO IMPROVE MAP EFFICIENCY B. Bucher, S. Mustière, L. Jolivet, J. Renard IGN-COGIT, Saint Mandé, France Introduction Standard APIs to visualise geodata on information infrastructures, like OGC MapContext (OGC 2005) or StyledLayer Document (OGC 2007), focus on specifying the map spatial extent, size and styled layers. The selection of styled layers mostly relies on portrayed features and on the layer acceptable resolutions. Theoretically, the selection of a styled layer could in a near future also rely on the nature of portrayed features based on semantic annotations of feature types in catalogues. But more criteria need to be considered when designing a map, e.g. what relationships between features should be visually rendered or what will be the ambient light. More generally, cartographers point out the relevance of relying on a map requirements to design more usable maps which include usable styles (Forrest 1999) (Chesneau et al. 2005)(Nivala et al. 2007) (Jakobsson 2002) (Stanek et al. 2007)(Bucher et al. 2007). There are two distinct issues addressed in this paper. First issue is that defining fixed styles, e.g. for each INSPIRE layer, that will be used on any map is a very challenging task if not impossible-. Yet, on the fly definition of adapted styles and feature portrayal is a costly process. A compromise is to define a registry of different styles for the same layers in order to adapt to different criteria regarding the final map. Second issue is that many new map makers usually have no academic background in cartography (Gartner and Peterson 2007). They may not always be capable of retrieving relevant styled layers for their map in a registry based on the existing styled layers description (feature types and styling rules); they need an abstract querying model. This also holds when the map maker uses a graphical client to build his map from existing layers flows. In this paper, we introduce both an abstract map specification model and a registry of predefined styled layers, focused on the adequate usage of colours in topographic maps. We illustrate the relevance of the different elements of our model based on three sources. The first one is the French Geoportail experience. The second one is the usability study performed by (Nivala et al. 2007). They have evaluated the usability of Web maps based on end user tests and on expert assessments. The third source is a study where we have extrapolated large scale topographic maps keys from 15 European countries to the French BDTOPO data model and applied the adapted keys to the same set of BDTOPO data.

2 Figure 1. Maps obtained by extrapolating to the same IGN dataset the styles of topographic maps from Austria, Norway and the Netherlands. Each map corresponds to a StyledLayersGroup in our registry. An abstract map specification model A first item of our proposal is a formal model for map specification that can be used by a novice map maker to specify the objectives of his map so that programs on the server side can help him retrieve (or define) efficient styles for his map and evaluate his map efficiency. This model is illustrated on Figure 2.

3 Profile age nationality gender activity <readers Context network support context> OBJECTIVES Map category emotional impact reference scales area CONTENT Domain nature : internalrelationship : Relationship type : Communication level type : order : FirstSight Reading1 Background StyledLayer DRAWING Figure 2. Map Specification model. In the following of this section, we explain the relevance of different criteria integrated in this model. One criterion is the relationships (association, dissociation, order) between features. There exist relationships between coloured objects that are intuitively interpreted by the reader into relationships between portrayed features (Bertin 1983). Similar hues convey a relationship of close natures, variation in intensity conveys a order relationship between thematic categories, and so on. Thus it is important to specify which relationships are relevant and should be portrayed on the map so that colours are selected and evaluated to render these relationships. (Nivala et al. 2007) have detected usability issues for MapQuest maps which used a similar colour for shopping areas and hospitals. With respect to this criterion, several styles for the same topographic layer are necessary to adapt to the overlay of thematic layers: the map maker should select a topographic background that does not use any colours too close to his layer colour. For example, on the French Géoportail, unfortunate graphical relationships occur when overlaying an avalanches layer over a topographic map because avalanches are portrayed with the same color as hicking tracks on the topographic layer (see Figure 3).

4 Figure 3. Overlay of two styled layers on the Géoportail : IGN topographic map and an avalanches layer. Another criterion is the respect of colour conventions to facilitate the interpretation of objects semantics: what colours are usually chosen to portray specific themes (water in blue) or to render specific properties (danger in red). (Nivala et al. 2007) detected for example usability issues related to the use of blue to portray motorway in MSN Maps and Directions whereas blue semantically refers to rivers. These conventions are not all fixed. They are sometimes specific to thematic domains, like the risk domain (Stanek et al 2007), and sometimes specific to local culture. In our European legend test, people (IGN employees) found it easier to read topographic maps with styles similar to IGN. This is why user profiles have been added in our map specification model; to select the relevant convention wrt user profiles and map domains. Another criterion is the relative importance of features on the map. In the study on European topographic legends, it is interesting to see how the resulting maps differ regarding the relative importance attached to different feature types. Like (Kent 2009), we believe this is an important interpretation of the landscape. Other criteria, much studied in ubiquitous mapping, are the profiles of readers and the expected reading conditions to read the map like the ambient light or the support (Jacobsson 2002). These elements have been integrated in our map specification model. A registry of predefined styles and styled layers associated to combination evaluation procedures

5 A catalogue of predefined styled layers is under construction. This aims at assisting a map maker in finding adequate styled layers for his map based on a query like like a topographic map for land planner engineers, with this specific featurecollection portrayed with this green pictogramme (see Figure 5). The catalogue references combinations of styles (FeatureStylesGroup) and combinations of styled layers (StyledLayersGroup). Importantly, an aggregate should not be created and documented automatically without specific evaluation mechanisms. The concept of FeatureStylesGroup is useful to store map templates. We introduce the attribute type of area for FeatureStylesGroup because a symbolisation may or may not be adapted to a given physical landscape. StyleProcessing Operation effect FeatureStylesGroup category emotional impact reference scales type of area domains relationships communication level user profile context Same descriptors as a map intentional and functional levels StyledLayersGroup emotional impact area domains relationships communication level context StyledLayer FeatureStyle FeatureCollection Figure 4. Catalogue model.

6 Figure 5. Two different FeatureStylesGroup applied to the same Feature Collections: in the second case, a user layer has been added. Specific operations must be implemented on the server side to retrieve layers. For example, if the map maker should use a user layer with fixed colours it is important to retrieve a topographic background which colours are the furthest from the user colour (illustrated Figure 5). References Chesneau, E., Ruas, A., Bonin, O., Colour Contrasts Analysis for a better Legibility of Graphic Signs on Risk Maps. in proceedings of the 22 nd International Cartography Conference, La Coruna, Spain Bertin, J., Semioloy of Graphics: Diagrams, Networks, Maps. University of Wisconsin Press, Madison Bucher B., Jolivet L., Buard E., Ruas A., The need for Web legend services, in J.M.Ware and G.E.Taylor (Eds), in proceedings of the 7th International Symposium on Web and Wireless GIS (W2GIS), Springer LNCS, Cardiff, UK Forrest, D., 1999, Developing rules for Map Design: a Functional Specification for a cartographic design Expert Sytem, Cartographica, vol 36 (3) Gartner G., Peterson, M., P. 2007, Experiences from hands-on webmapping workshops of the ICA commission on map and the internet, in proceedings of the 23 rd International Cartographic Conference, Moscow, Russia

7 Jakobsson, A., 2002, User requirements for mobile topographic maps, GiModDig project IST deliverable D2.1.2 Kent, A., J., Cartographic blandscapes and the new noise: finding the good view in a topographical mashup, The Bulletin of the Society of Cartographers, Vol 42 Nivala, A.-M., Brewster, S.A., Sarjakoski, L.T., 2007, Usability Problems of Web Map Sites. in proceedings of the 23 rd International Cartographic Conference, Moscow, Russia Open Geospatial Consortium (OGC), Web Map Context Documents, OGC Implementation Specification, Sonnet, J. (Ed) Open Geospatial Consortium (OGC), Styled Layer Descriptor profile of the Web Map Service Implementation Specification, v1.1, OGC Implementation Specification, Lupp, M. (Ed) Stanek, M. Konecny, L. Friedmannova, 2007, An Adaptive Cartographic Visualisation for Support of the Crisis Management, in proceedings of the 23 rd International Cartographic Conference, Moscow, Russia