SMART LEGEND SMART ATLAS !

Atlases are moving quickly towards multimedia, three-dimensional visualization and interactive techniques. Digital atlas maps benefit from nearly free navigation, sophisticated visualization techniques and analytical functionality. Zooming and panning, coloring, and interactive queries are standard features nowadays. But one of the most important features of every map  the legend  still lacks appropriate functionality and even good graphic design. Reviewing traditional and digital map legends, seven functional components can be extracted: visualization, navigation, analysis, dimensionality, thematic issues, general information, and layout. These seven legend components should be considered in the design process of every interactive legend. But we can go even a step further, by imagining and realizing smart functionality for the legend. In our new smart legend approach, the legend is defined as a central control unit of the map. We can distinguish two main feature categories of a smart legend; Self-acting adaptations of the legend that aim at a preferably optimal depiction of the map elements, and the range of user interaction features provided. 1 THE LEGEND, A CLASSIC MAP FEATURE Traditional legends in paper maps and atlases Map legends are traditionally appointed to explain the content of a map. According to the Kansas Association of Mappers (2005), the legend is defined as An explanation of the symbols, codes, names given to variables and other information appearing on a map drawing or chart. It includes a sample of each symbol, line pattern, shading, or hatching appearing on the map along with annotations describing the meaning of each.  In other words, it is an important map feature -the symbol key used to interpret a map that lists and explains all groups of map elements. Figure 1: a) Placement of traditional map legend (population density), b) Legends with point or line raster overlay (geology; Swiss World Atlas 2004) On printed maps, the legend is often placed in the blank space of the map and is divided into several parts (fig. 1a). It usually contains various legend elements: heading and labels, legend boxes or symbols to depict numerical values or nominal classes, class units, and explanatory text. By browsing through some printed examples, we found legends with only point elements, linear features or areas, or any combination of point, line, and area. Legends with point or line raster overlay allow further differentiation of a certain layer (fig.1b). Sometimes, the map title and map scale, origin, orientation, and other map information are also incorporated into the legend box. Graphically, the legend elements are designed according to the symbolization of the elements as they appear in the map. Advantages: Printed map legends are usually explanatory to the full extent, with the application of complex sophisticated graphics, and a strong trend to illustrative characteristics. Shortcomings: The placement of the legend or its parts seems to be steered by the empty space available. It is often situated far away from the corresponding map element, and the colors are neither distinguishable nor assignable (e.g., geology map with hundreds of layers). 2 DIGITAL LEGENDS: HOW POWERFUL ARE THEY? Interactive legends may be presented in two different ways (Lobben and Patton 2003); first, information about base map and thematic elements may be imbedded in the map. Second, a static or interactive legend panel provides information in a figurative and textual way. While the first way provides specific information about individual map elements, the second method  using map legend panels  works in a more general sense and usually addresses groups of map elements. In this paper, we concentrate on legends in a separate display area because of their higher potential for visualization and analysis. Digital legends With digital maps and atlases on CD-ROM, DVD and on the Web, the map legend is usually treated as an image. The legend is either scanned from a printed original or drawn and compiled digitally with the intention of acting as an integrated whole. Thereby, the legends symbolization is often fairly good but it lacks of real interactive techniques (fig. 2a). Interactivity is reduced to some simple windows techniques, which make the legend movable, scalable, and scrollable (fig. 2b). More complex digital legends are organized in a hierarchical structure, often accessible by means of a pull-down menu. Advantages: The legend as a whole is very mobile; scanned graphics are appealing. Shortcomings: Poor graphic quality using GIS standard legends and no interaction with the map itself is prevailing. Figure 2: a) Figurative graphics in a digital legend (Digital Wisdom 2005), b) Digital legend using window techniques (Oakville GIS Center 2005). Interactive legends Real interactive legends are actually able to partly modify the appearance of the map and to perform some basic information retrieval. Three different groups of actions can be distinguished: a) actions on embedded information in the map, b) actions in the legend, and c) bidirectional actions. Actions on embedded information in the map contain interactive querying by mouse rollover or clicking on the map. It will highlight a specific map class in the legend (Miller 1999) or evoke a panel with individual map element information. Legend information embedded in the map display may also contain sound or a day/nighttime context (Kraak et al. 1997). Actions in the legend will change the background of legend boxes, so that legend colors correspond to the map coloring (e.g., when combining map colors with relief shading). With a click in a legend symbol box, the user gets text information about the topic (fig. 3). The interactive legend can also be structured according to hierarchy (Lobben and Patton 2003). While the first hierarchic level includes the most general classes, the second level will reveal a subset of each class. By clicking on the general class label or symbol this second level can be assessed. As an additional possibility, Peterson (1999) suggests the idea of animation steering: The legend, implemented as explanatory boxes, provides a way both to control the animation and determine its meaning. Square boxes or slices of a circle are assigned to several points in time. Switching between these squares or slices allows different types of animations. Kraak et al. (1997), also point out the exploration and interaction potential of animation processes by means of interactive legends. Kumar (2004) recommends frequency histogram legends for classed and unclassed choropleth maps. It may be possible to change class intervals, class limits and schemes of classification (quantile, equal interval, equal area etc.). According to his research, frequency histogram legends are appropriate to assess statistical distribution. In various atlases like the Atlas of Germany (2004) and the Dutch Wereld Atlas (1999), the legend allows to modify the maps appearance, especially its colors and classes. Figure 3: Amplified use of the legend symbol box (Environment Canada 2005). Bidirectional actions are activated both in the legend and in the map at the same time. As a supplement to simple legend boxes, a histogram of every single map value or each category, incorporated in the legend, can work in the bidirectional way. Querying a value in the legend will show the corresponding map element and vice versa (fig. 4). Figure 4: Bidirectionally linked frequency histogram/diagram of map values (Stopper 2005). Advantages: The assignment of map elements in the legend is always clearly visualized, sometimes even in a bidirectional way. The graphic appearance of the map and the classification of the data are modifiable. Shortcomings: The legends graphic appearance needs to be improved, because interactive legends are in most cases non-figurative and designed with a high degree of abstraction. The features characterized above are very often only fundamental sketches, but are not yet running operationally in commercial products. Interactive legend techniques in the «Atlas of Switzerland 2.0» The «Atlas of Switzerland» is basically designed to give the user amplified active control over the visualization process. In its second version «Atlas of Switzerland 2.0», published in November 2004, several interactive legend features have been integrated. Considering layout issues, the legend is designed as a permanently available fold out panel and is easily assessed by means of a register. It therefore appears and disappears by clicking on a tab. It is forced to close if another panel is opened claiming the same place/space. The legend module is even linked to the print module: the legend will only be printed if the map legend is open. The «Atlas of Switzerland 2.0» applies the dual thematic layer concept where the user can choose an additional map layer. The legend will then be split up in two separate parts, in an active map layer and a passive map layer. To switch a layer from passive to active, the user has just to click in the passive part of the legend. If the legends size exceeds the maximum space available, the passive legend part is automatically closed, but still can be reopened and activated by clicking on a radio-button. Bidirectional queries are indicated by highlighting the corresponding map class in the legend while querying the thematic elements of the active map layer. For complex map issues like geology, with an exhaustive number of categories, a hierarchical legend has been designed. This makes it possible to show all categories of the map at once and simultaneously focus on a specific category (Huber and Schmid 2003). In addition, a category selection tool is integrated in the map legend; clicking on one or more legend category or its color boxes makes the other legend categories fade to gray (fig. 5a). This function applies on vector and raster maps and enables the u