Using SVG-based Maps for Mobile Guide Systems

A Case Study for the Design, Adaptation, and Usage of SVG-based Maps for Mobile Nature Guide Applications

Keywords: mobile nature guide, adaptable maps, location based service

Vilma Patalaviciute
Institute for Applied Computer Science, Forschungszentrum Karlsruhe
76344 Eggenstein/Leopoldshafen


Vilma Patalaviciute has studied geography and cartography at Vilnius University in Lithuania. Currently she is Master Student of Geomatics at University of Applied Sciences in Karlsruhe and works on her master-thesis in Forschungszentrum Karlsruhe, Germany.

Dr. Clemens Düpmeier
Institute for Applied Computer Science, Forschungszentrum Karlsruhe
76344 Eggenstein/Leopoldshafen


Dr. Clemens Düpmeier obtained his diploma in mathematics from the Ruhr-Universität in Bochum (Germany) and his PhD in Computer Science from the University of Koblenz in Germany. He is currently working as a computer scientist at the Institute for Applied Computer Science of the Karlsruhe Research Center (Germany), where he is speaker of the "web-based information systems and databases" program of emphasis. His research interests include web-based informations systems, mobile applications, service driven networks and distributed systems. Dr. Clemens Düpmeier is also an assistant professor at the Department of Information Technologies of the Berufakademie Karlsruhe (University of Cooperative Education Karlsruhe) in Karlsruhe, Germany.

Prof. Dr. Peter Freckmann
Department of Geoinformation, University of Applied Sciences Karlsruhe, Germany
Moltkestraße 30
76133 Karlsruhe Prof. Dr. Freckmann


Prof. Dr. Freckmann is Professor at the Department of Geoinformatics at the University of Applied Sciences Karlsruhe. He is head of the Masters Degree Programme in Geomatics. His interests are Spatial Visualisation, Cartographic Models and Geo-Information-Systems.

Markus Ruchter
Institute for Applied Computer Science, Forschungszentrum Karlsruhe
76344 Eggenstein/Leopoldshafen


Markus Ruchter obtained a degree in Environmental Sciences from the University of Essen, Germany and is currently working on his Ph.D. at the Institute for Applied Computer Science, Forschungszentrum Karlsruhe, Germany. His thesis deals with the development of mobile guide systems for environmental communication and education.


Maps are a fundamental component of mobile guide systems, providing navigational assistance, as well as access to information offered by other location-based services. Accordingly, in mobile nature guide systems maps have to provide navigational assistance in remote environments providing very few additional orientation clues. Thus, the map becomes a central component of the interface that is expected to offer guidance as well as interpretation of the natural environment, while distracting the user as little as possible from his actual leisure experience. This calls for mobile maps which are adaptable to the needs and abilities of different target groups as well as a highly dynamic natural environment. A number of concepts are proposed for the design of mobile maps, which can help to meet the challenges of mobile nature guides. These include for instance the provision of additional navigational assistance by using natural landmarks, or the dynamic adaptation of the colour scheme of the map to match the seasonal changes. A case study of the Mobile Nature Guide (MobiNaG) system will illustrate the application of SVG in a mobile guide system and will in particular demonstrate how SVG-based maps can be designed and implemented to realize the proposed concepts.

Table of Contents

1. Introduction
2. Mobile guides and SVG-based Maps
     2.1 MobiNaG Architecture and usage of SVG in the prototype
3. Maps for Mobile Nature Guides
     3.1 Navigational assistance by means of natural landmarks
     3.2 Personalized maps for a self-determined nature experience
     3.3 Adaptable maps matching the dynamics of the natural environment
     3.4 Interpretative maps - encouraging interaction with nature
     3.5 Zoom level and map legend
4. Summary and outlook

1. Introduction

There is an increasing number of mobile guide systems, which provide users with Location Based Services (LBS) during recreational activities like sight seeing tours through cities ([Cheverst et al. 2000]) or museum visits ([Oppermann, Specht 2000]) ([Baus et al. 2005]). It is a fundamental feature of such systems to provide the user with navigational assistance usually by means of mobile maps and position determination ([Kray, Baus 2003], [Baus et al. 2005]). Besides providing navigational support, maps in mobile guidance systems fulfil another crucial role. They serve as means of interaction ([Baus et al. 2005]) and become part of the user interface, granting access not only to geographical information but also to the information offered by other location-based services.

The designers of mobile guides have to deal with a variety of constraints. These include technical resources such as storage capacity, bandwidth, computational power and display size, as well as non-technical factors like a constantly changing environment and especially the cognitive resources of the user employing the system as a tool for completing another task ([Meng, Reichenbacher 2005]). Thus in order to adequately assist the user during his leisure time experience a mobile map should only include the information that is instantly needed and effortlessly comprehensible as well as intuitive means of interaction with the LBS ([Meng, Reichenbacher 2005]). This implies that the mobile map service needs to take over an essential part of the mental effort of the user, adapting itself to the user’s context ([Meng, Reichenbacher 2005]).

While a number of systems have addressed these issues for mobile guides in urban environments as well as exhibition or fair settings ([Baus et al. 2005]), there have only been a few systems built to guide the user through natural areas ([Düpmeier, Ruchter 2004]; [Burghardt et al. 2003]). The Mobile Nature Guide (MobiNaG) is such a mobile guide system specifically designed as an instrument for environmental communication in natural areas. MobiNaG is a project carried out in cooperation with the Naturschutzzentrum Karlsruhe-Rappenwört, an environmental education institution in Karlsruhe, Germany. As a visitor center to a floodplain conservation area along the Rhine River, it is an ideal test bed for the prototyping and evaluation of MobiNaG. The main goal of the MobiNaG project is to create a mobile guide software that not only provides location based tourist services including plain factual information but also assist the user in learning more about his natural environment by encouraging him to explore and interact with natural phenomena. For such a mobile nature guide system afore mentioned requirements regarding mobile maps constitute a particular challenge. Maps in mobile nature guide systems have to provide navigational assistance in remote environments, which provide very few additional orientation clues like street signs or prominent buildings and frequently there are not even passers-by who could be asked for directions. Under these circumstances the map becomes a central component of the interface to the system that is expected to guide the visitor through an unfamiliar environment providing him with a challenging but pleasurable experience (which should certainly not include the experience of getting lost). At the same time, serving as a tool, the map should divert as little of the user’s attention as possible from his main task, exploring his natural environment with all his senses. Moreover, a map for a mobile nature guide should not solely offer geographic information by means of an abstract representation of the environment but it also needs to help the user to identify and comprehend natural features that he can observe in the real world.

The adaptation of maps to the user’s context as proposed by Meng and Reichenbacher ([Meng, Reichenbacher 2005]) is somewhat more complex in a remote natural area than in a more static urban setting, where the change might be mainly induced by the alteration of the user’s position. As the natural environment is highly dynamic, which is especially apparent in the seasonal changes, distinctive environmental context features have to be taken into account, such as the season of the year, light and weather conditions as well as the presence of typical plants and animals ([Düpmeier, Ruchter 2004]).

In this paper a number of concepts will be proposed that can resolve some of the issues related to the design of highly adaptable maps for mobile nature guides. Since some of these concepts have already been implemented in the MobiNaG research prototype using SVG technology particularly for the display of maps, some SVG related implementation aspects of these concepts will be discussed too. So, at the end of the paper a conclusion could be drawn, how well SVG lends itself to the implementation of the map interface in the MobiNaG prototype.

2. Mobile guides and SVG-based Maps

Existing mobile guides use different types of maps ranging from simple black and white sketches over 2D-maps similar to paper maps (e.g. Lol@) to animated 3D-maps (e.g. TellMaris and BPN) ([Baus et al. 2005]). Several of these guide systems like for example PARAMOUNT ([Wittmann, Loehnert 2002]) and Lol@ ([Uhlitz, Lechthaler 2002]) use raster data for these maps. While raster data based maps are easy to implement, Reichenbacher ([Reichenbacher 2002]) argues that a vector based approach has several advantages over the raster format, such as smaller file size and higher flexibility in respect to dynamic modification and adaptation of the map to different context situations, which will be honoured in the mobile environment as has been pointed out in the introduction.

SVG has been discovered by a variety of projects as a vector graphics format particularly suitable for the implementation of maps on the web as well as on mobile devices ([Reichenbacher 2002], [Pavlicko, Peterson 2004]). The scalability of a vector graphics format guarantees that no information is lost while zooming, because SVG based map objects, such as text labels, can be easily scaled to stay readable at other zoom steps, an essential feature on a device with a small display. Furthermore, scripting SVG using the Document Object Model (DOM) makes it possible, to dynamically change maps in nearly every aspect imaginable, like adding or deleting map objects and layers, changing visual attributes of the map objects etc. This allows for an easy implementation of highly adaptable maps as will be shown in this paper.

Because an event model is integrated into the SVG DOM, it is also possible to create highly interactive maps in SVG ([Reichenbacher 2002]). Finally, with regard to the limited technical resources of mobile devices SVG has another key advantage: the size of SVG based maps is generally small.

A few mobile guide applications (like SaiMotion, GiMoDig) already use SVG for the generation of maps ([Bieber, Leck 2003]). Especially in the GiMoDig project the Geographic Markup Language (GML), another XML format for describing the data semantics of map objects, is used for storing and distributing geographical data while SVG is used for the presentation of maps ([Harrie, Johansson 2003]).

2.1 MobiNaG Architecture and usage of SVG in the prototype

Because of the many advantages of using SVG for the display of maps, it was decided that next to other XML technologies, SVG should be used as one central implementation technology for MobiNaG. The first version of MobiNaG was implemented as a research prototype for the evaluation of the concepts for such nature guide applications. Due to the fact that SVG also allows the creation of 2D-interaction elements it seemed reasonable to implement not only the map but also most of the map related user interface in SVG. This also provided an interesting opportunity to examine if a user interface solely based on SVG technology could lead to a more natural user experience in contrast to a classical GUI application only embedding a SVG component for the map view. This led to the architecture for MobiNaG as shown in Figure 1 ([Düpmeier, Ruchter 2004]).


Figure 1: Architecture of the mobile guide software MobiNaG

Following the familiar model-2 architecture for web applications, the C++ application is separated into a controller component, a view generating template engine and different components which define the model logic of the application. The user interface of the application is rendered in form of different SVG screens by a C++ SVG rendering component (eSVG), which also accepts any interactions of the user with the SVG based user interface and forwards them to the central controller component of the C++ application. Application logic components, such as the navigation manager, POI manager or tour manager register in the controller to intercept certain SVG interactions directed to them, and process them based on data describing the context of the application (such as nature area visited, GPS location information or the user’s profile).

The components use a well defined SVG generation interface (called Template Engine in Figure 1) to perform changes in the SVG DOM tree. These DOM changes can be used to deliver information to the user by changing parts of the SVG based user interface, such as the map view or rendering a popup window with a textual notification for the user. The SVG generation interface is called template engine because it can use templates of SVG code, which get filled in by application data and are then transformed into DOM tree changes of the eSVG engine resulting in complex changes, like adding a complete layer, of the SVG interface.

Beside the possibilities to change the DOM tree of a displayed SVG document directly over the eSVG component API, the eSVG C++ component also allows it to execute arbitrary javascript functions, defined in the SVG document itself, from within the application. As a consequence it is possible to define entire user interface elements (like for instance a popup notification window or tooltip label) as javascript implemented user interface objects. These objects can be stored in a user interface library linked to the SVG document and called from the C++ side by executing javascript code fragments, which will be interpreted by the eSVG component’s javascript interpreter. As has been pointed out, SVG can in general be utilized as the building language for graphical user interface elements. This paper however will focus on using SVG for maps and SVG-based user interface elements are only discussed with respect to elements needed for interactive features of the map screen itself.

As has been discussed above changes in the displayed map, following a user interaction or context change can be achieved from the C++ application by either changing the SVG DOM directly through the C++ DOM API of the eSVG component or by calling javascript functions from within the application. In some cases however a user’s request could be easily achieved by only calling a javascript function within the SVG document itself. This includes interactions like zooming of the map as well as displaying or hiding certain objects or layers, as will be shown in the next sections.

3. Maps for Mobile Nature Guides

As has been discussed in the introduction, it is one of the objectives of the MobiNaG project to use highly adaptable and intuitive maps in nature. As a prerequisite for an adequate personalization as well as adaptation of the mobile map, it is necessary to take a closer look at the context related to the exploration of natural areas. The context model for mobile nature guides as proposed by Düpmeier and Ruchter ([Düpmeier, Ruchter 2004]) includes four primary context types. The geographical context subsumes the relevant geographical information such as the location of Points of Interest (POIs) or routes that can be taken. All aspects related to the user, like his demographic profile and particular interests related to nature, are defined by the user context. The environmental context comprises the distinctive environmental aspects, which are relevant for the exploration of a natural area, including environmental resources and conditions as well as the time of the year.

Based on this assumption of context-awareness, a number of concepts for the design of maps for a mobile nature guide have been developed.

3.1 Navigational assistance by means of natural landmarks

With this concept one of the key issues regarding mobile nature guides, the provision of navigational assistance in natural areas, could be addressed. Comparable to other mobile guides MobiNaG uses a mobile map along with a position determination and tracking mechanism to inform the user about his current location and his navigational history. The positioning and tracking mechanism provided by the MobiNaG navigation service uses data from a Global Positioning System (GPS) receiver connected to the device to show the users current position. If the user is within the reach of a certain tour station, a popup notification box appears on the map and the user is alerted by an audio signal. He can then request more multimedia information about the reached tour station by clicking on an Infos button in the popup (Figure 2). Due to the fact that apart from the receiver unit no other network infrastructure is needed, GPS lends itself very well for the positioning in remote and natural areas.


Figure 2: Basic MobiNaG navigation screen with station symbols and notification popup

Nevertheless GPS positioning comes with certain restrictions. The quality of the received satellite signal varies depending on the environmental conditions (weather conditions, shading by tree canopy, etc.). As a consequence the accuracy of the positioning also varies and the mechanism may even fail leaving the user without the crucial navigational assistance. Because of these issues, the map for a mobile guide system has to provide additional orientation cues to the user allowing him to find his current location without technical support in the case that the GPS position is not available or accurate enough.

Furthermore, observations during an ongoing field trial of the MobiNaG system indicate, that many of the test subjects had difficulties to make navigational decisions on intersections if no additional navigational instructions were provided, even with the positioning indicator in operation. Ross et al. ([Ross, May 2004]) have proposed that the use of landmarks can improve the navigational assistance of guide systems. This concept could also be of great use in mobile nature guides to deal with the discussed issues. However, while in urban environments the user encounters a diversity of additional navigational cues like for instance a street sign or a prominent building like a church; natural environments frequently lack similar features. For first time visitors the trees in a forest may all look the same, thus it is a challenge for the designer of mobile nature maps to find suitable landmarks. At the test site of the MobiNaG system, the flood plain forest conservation area, benches, information panels and piles of deadwood were identified as some outstanding features that should serve the user as additional orientation cues along the selected route. Designed based on the recommendations of Elias et al. ([Elias et al. 2005]) on the visualization of landmarks, such objects can be added to the map of the mobile nature guide (see Figure 3) as additional navigation hints. The concept is currently evaluated at the test site. In any case: when using prominent natural features as landmarks, the designer of mobile maps has to take the dynamics of a natural environment into consideration. Objects such as piles of deadwood can for example be removed at any time thus the landmarks may need to be frequently updated.

Furthermore, landmarks add more details to a map. As has been previously mentioned, because of the limited size of the display and the user’s attention to other tasks, it is not recommended to show too many details at a time on a mobile map. In order to avoid visual cluttering or cognitive overload landmarks are only added at bigger zoom steps in MobiNaG where they don’t add too many details to the shown map part (see Figure 3). This selective display of the landmarks only at certain zoom steps can be implemented easily in SVG because only the value of the visibility attribute of the landmark objects needs to be changed from ‘hidden’ to ‘visible’ in the javascript zooming function.


Figure 3: Landmark based navigation

3.2 Personalized maps for a self-determined nature experience

As it has been proposed by Meng and Reichenbacher ([Meng, Reichenbacher 2005]) the mobile map service needs to take over an essential part of the mental effort of the user in order to provide a pleasurable and intuitive experience. This can be achieved by personalizing the map such that based on an user’s profile only the information that is needed by the particular user is displayed using a representation of the real world object, that the user can easily comprehend.

The MobiNaG project uses a set of different user profiles, corresponding to a selection of target groups which resulted from a front-end evaluation. These target groups are high school students (children and young adults of the age 6-17), families with children and adults interested in nature ([Düpmeier, Ruchter 2004]). A prior paper prototyping study in the field indicated that there is not only a difference in the comprehension of interface elements between children and adults, but that the adults should be further subdivided into two subgroups. One group comprising the younger adults of the age18 through 49, whereas the older adults above the age of 50 should be grouped separately as they were frequently less experienced with regard to the usage of computers and especially mobile devices ([Düpmeier, Ruchter 2004]). In general for the design of maps for mobile nature guides it needs to be considered that the target groups usually consist of first time or non-expert users with limited map reading capabilities and computer expertise.

One concept for the personalization of maps for MobiNaG implies the representation of POIs by using target group specific symbols. Figure 4 illustrates some examples of these different symbols for the 3 different target groups mentioned above. Symbols for high school students and families are designed in a detailed 3D style. These symbols were designed as realistic and aesthetically pleasing as possible taking into account that children need a less abstract visualization and are frequently accustomed to a graphically rich game like interface. Families and children were subsumed in one group as parents commonly engage in a family activity with the intention to provide their children with a pleasurable experience. According to the experience from the paper prototyping study ([Düpmeier, Ruchter 2004]), adults frequently focus less on hedonistic aspects but value foremost the readability of icons. Thus the symbols for adult groups are more generalized and abstract 2D icons providing a high level of contrast. The icons for the “older” user (above 50 years) are additionally increased in size, assuming that older people have frequently difficulties with reading the small signs. Default symbols, which are to be displayed if no user profile was specified, will match the symbols for adults (18-50).


Figure 4: Examples of different symbols for different target groups

In MobiNaG personalization is being implemented by means of providing the user with a selection of guided nature tours adapted to the interests and needs of the respective target groups. When a chosen tour is loaded, the system internally knows what target group is associated with this tour. It will then select the logical description of the POIs pertaining to the selected tour, such as the stations of this tour, from a POI description XML file of the natural area and will dynamically create a new SVG layer into which the POIs represented by the corresponding icons will be loaded. The POI icons for a given POI class are instantiated by an SVG use element from a SVG-based icon library by referencing the symbol by an xlink:href attribute. The use element is positioned accordingly to the world coordinates of the POI as given by the logical POI description. Because the system knows the designated target group when the tour is loaded, different icons sets (icon libraries) can be chosen just by changing the base url in the xlink:href attribute in respect to the target group. Furthermore, different tours will include different multimedia contents displayed in MobiNaG.

Tours could also be associated with other personalization criteria, like for instance the users interest with regard to his natural environment. There are users visiting natural areas who are more interested either in plants or in animals. Accordingly during their exploration they will preferably look for a tour with either floristic or faunistic phenomena. Based on a corresponding classification of the tour content the map of the mobile nature guide could also be adapted to the content class. Hence details on the map will differ such that for spare time botanists many details about trees and other plants will be displayed on the map, while information about the fauna will be more generalized and vice versa. Figure 5 shows an example in which the same area is visualized differently depending on the interests of the user.


Figure 5: Different visualizations of the test area depending on interest of the user: default view (left) and map for user with special interest in fauna (right)

3.3 Adaptable maps matching the dynamics of the natural environment

As has been initially discussed, a map for a mobile nature guide should provide more than just abstract geographical information. The map should adequately represent the natural environment even if the environmental context is altered. An apparent example for the dynamics that the natural environment in temperate climates undergoes is seasonal changes. With the change of seasons the appearance of nature changes which is most noticeable in the differences in predominant colors. Because of the color of the vegetation the visual impression of the whole natural area varies. In the spring the predominant color is light green, in the summer dark green, while in the fall it is yellow and orange and in the winter gray and brown. This impression of the visual changes in nature is visualized in the MobiNaG maps by changing the color scheme of the maps to match that of nature (see Figure 6). This can be easily achieved with SVG based maps by loading the map with different style sheets based on the current time information of the mobile device.


Figure 6: Visualization of nature phenomena based on season of the year: spring (left) and fall (right)

3.4 Interpretative maps - encouraging interaction with nature

Beyond providing navigational assistance, maps for a mobile nature guide should serve as an interface between the user and the system but also between the user and the natural environment. An interpretive map should be designed to guide the user to certain environmental phenomena. The symbol for a phenomenon may either give a realistic representation of an object or may also provide simple instructions for a first hand experience of the natural environment. Figure 6 includes the example of a nature awareness trail. A series of POIs is displayed using symbols that instruct the visitor how to experience nature at these locations with different senses (e.g. smell, touch and feel, observe, listen). While visualizing this kind of interpretive information, the mobile nature guide map again has to account for the dynamics of the environmental context. Which nature awareness activity may be appropriate at a specific location may change depending on the season. For example, one of the POIs on the map in Figure 6 (left) indicates the location of a large wood garlic population, which emits a very strong aroma in the spring. In this case the user will be encouraged by an icon representing a nose to smell the characteristic odor. In the fall this odor is long gone but then the same location may be a good place to observe migratory birds landing on the oxbow of the river Rhine (Figure 6, right).

3.5 Zoom level and map legend

On a small screen device the user can not look at a map of a larger area at its full extend while all information is displayed at the same time. This inevitably leads to visual cluttering hindering the effortless usage of the system. Harrie et al. ([Harrie et al. 2002]) point out that while navigating users need in turns a map at a large scale as well as at a small scale. One option to resolve this problem is to provide a zooming as well as a panning mechanism that allows the user to handle the map according to his needs. The map for the MobiNaG system can be viewed at three different zoom levels, which in case of the test site correspond approximately to map scales in 1:25.000, 1:10.500 and 1: 4.500. The first zoom level (scale 1:25.000) represents an overview of the natural area. At the following zoom levels more details are dynamically added to the map providing the user with representations of POIs as well as landmarks. If the map is used at a large scale the user can change the visible area by panning it into a desired direction.

Zooming and panning has been realized in MobiNaG by changing the viewport of the section of the map displayed with javascript functions implemented within the SVG document without the intervention of the surrounding application. While panning is straight forward the zooming function has to take into account that different POI layers will be dynamically shown or hidden on the map according to the given zoom steps. Also, because the size of the POI icons should be the same in all layers, they have to be rescaled for the different zoom steps. The same is true for the position indicator as well as the tracking path indicating the navigational history.

Next to the dynamic adaptation of the map based on the context of use, the user can to some degree also determine himself, which information will be displayed on the map. For this purpose the MobiNaG system offers an interactive legend (see Fibure 7). Apart from providing explanations on the symbols used, the user has the possibility to switch the visualization of each feature on or off in the legend popup window.


Figure 7: Interactive map legend in MobiNaG

This popup is implemented as an SVG only layer which is dynamically displayed when the legend icon is clicked in the map toolbar at the bottom of Fibure 7, which is also entirely implemented in SVG. Each check box is associated with a javascript function, which dynamically switches the visibility of the corresponding POI layers on or off.

4. Summary and outlook

This paper has shown that the dynamic adaptability of maps is a crucial feature of mobile guide applications. Mobile guides are faced with the limitations of small screen devices, which results in the necessity to display information on maps only when needed in order to avoide visual clutter by overlapping map objects as well as cognitive overload by showing too many details.

In the context of the MobiNaG project concepts for such adaptable maps designed for mobile nature guides are explored and evaluated based on a first research prototype using SVG-based maps. According to the experiences presented in this paper, SVG seems to be a suitable implementation technology to achieve such highly adaptable maps.

The evaluation of the prototype system has also demonstrated that the performance of some map based user interactions in the MobiNaG research prototype (like adding a new layer with many POIs to an existing map) is still critical with regard to the user satisfaction. However with the computational power of mobile devices constantly increasing, this limitation should be overcome in the near future and the SVG based map implementation will show its full strength. At the same time the MobiNaG research prototype is being redesigned and optimized for a first production version. For this production version further adaptability features will be implemented using SVG as the basic implementation technology for map display.


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