12 Geographical Data Visualization on Mobile Devices
265
Zipf [38] provides a comprehensive overview of the design steps involved in
adaptive map generation, considering a wide range of variables such as user preferences and interests, tasks, cultural aspects, communicative goals, and current context
and location. For example, the orientation of a map can be adapted so that the map
is aligned in the direction the user is walking, thus simplifying navigation of an
environment, while the meaning of colors can be taken into specific account when
generating maps for different cultures.
One of the design steps identified by Zipf and investigated by different authors is shape simplification through generalization. Generalization is a graphic- and
content-based simplification of the data presented on a map that aims at abstracting
irrelevant details to reduce the cognitive effort of the user, and at simplifying the process of creating a lower scale map from a detailed one. As reported in Chaps. 4 and
5, generalization techniques can also be used to support progressive transmission of
vector data through wired or wireless networks, albeit studies in this direction for
mobile scenarios are still at an early stage.
Agrawala and Stolte [1] developed some techniques for the generalization of
cartographic data that improve the usability of maps for road navigation on mobile
devices. Standard computer-generated maps are difficult to use because their large,
constant scale factor hides short roads and because they are usually cluttered with
extraneous details such as city names, parks, and roads that are far away from the
route. The techniques proposed by Agrawala and Stolte are based on cognitive psychology research showing that an effective route map must clearly communicate all
the turning points on the route and that precisely depicting the exact length, angle,
and shape of each road is less important. By distorting road lengths and angles and
simplifying road shape, it is possible to clearly and concisely present all the turning
points along the route in less screen space. The generalized maps that are obtained
exaggerate the length of short roads to ensure their visibility while maintaining a
simple, clean design that emphasizes the most essential information for following
the route. These generalized maps can fit to the display size of a PDA by rotating the
entire route so that the largest extent of the map is aligned with the vertical axis of
the page, thus providing extra space in the direction the route needs it most.
Generalizing map features is a useful approach to simplify the display of maps
on the small screen of mobile devices, but maps can still be too large to fit into the
available screen space. Thus, several techniques have been proposed in the literature
to visualize large maps on mobile devices.
A basic approach is to display only a portion of the map and to let users control
the portion shown by conceptually moving either a ‘viewport’ on top of the map, or
the map under the viewport. Scrollbars are typically used to support this interaction,
providing separate vertical and horizontal viewport control. Another mechanism is
panning allows users to drag the map in any direction without any constraint on the
movement. It is also common to provide users with a zooming function that allows
one to increase or decrease the size of the visible portion of the map [16]. Alternative
interaction techniques have been developed to simplify these operations on mobile
devices. Jones et al. [19], for example, present a technique that combines zooming and scrolling into a single operation, depending on how much users drag the
265
Zipf [38] provides a comprehensive overview of the design steps involved in
adaptive map generation, considering a wide range of variables such as user preferences and interests, tasks, cultural aspects, communicative goals, and current context
and location. For example, the orientation of a map can be adapted so that the map
is aligned in the direction the user is walking, thus simplifying navigation of an
environment, while the meaning of colors can be taken into specific account when
generating maps for different cultures.
One of the design steps identified by Zipf and investigated by different authors is shape simplification through generalization. Generalization is a graphic- and
content-based simplification of the data presented on a map that aims at abstracting
irrelevant details to reduce the cognitive effort of the user, and at simplifying the process of creating a lower scale map from a detailed one. As reported in Chaps. 4 and
5, generalization techniques can also be used to support progressive transmission of
vector data through wired or wireless networks, albeit studies in this direction for
mobile scenarios are still at an early stage.
Agrawala and Stolte [1] developed some techniques for the generalization of
cartographic data that improve the usability of maps for road navigation on mobile
devices. Standard computer-generated maps are difficult to use because their large,
constant scale factor hides short roads and because they are usually cluttered with
extraneous details such as city names, parks, and roads that are far away from the
route. The techniques proposed by Agrawala and Stolte are based on cognitive psychology research showing that an effective route map must clearly communicate all
the turning points on the route and that precisely depicting the exact length, angle,
and shape of each road is less important. By distorting road lengths and angles and
simplifying road shape, it is possible to clearly and concisely present all the turning
points along the route in less screen space. The generalized maps that are obtained
exaggerate the length of short roads to ensure their visibility while maintaining a
simple, clean design that emphasizes the most essential information for following
the route. These generalized maps can fit to the display size of a PDA by rotating the
entire route so that the largest extent of the map is aligned with the vertical axis of
the page, thus providing extra space in the direction the route needs it most.
Generalizing map features is a useful approach to simplify the display of maps
on the small screen of mobile devices, but maps can still be too large to fit into the
available screen space. Thus, several techniques have been proposed in the literature
to visualize large maps on mobile devices.
A basic approach is to display only a portion of the map and to let users control
the portion shown by conceptually moving either a ‘viewport’ on top of the map, or
the map under the viewport. Scrollbars are typically used to support this interaction,
providing separate vertical and horizontal viewport control. Another mechanism is
panning allows users to drag the map in any direction without any constraint on the
movement. It is also common to provide users with a zooming function that allows
one to increase or decrease the size of the visible portion of the map [16]. Alternative
interaction techniques have been developed to simplify these operations on mobile
devices. Jones et al. [19], for example, present a technique that combines zooming and scrolling into a single operation, depending on how much users drag the