Visualization Functions

The user interface of a Spatial OLAP tool provides unique capabilities to explore spatial data in an intuitive and interactive way. The capability of linking or synchronizing several views of the same information in a context of interactive exploration of data brings new possibilities to benefit from current research in geovisualization.

Some visualization functions of an ideal SOLAP technology will be presented here: various display types, display synchronization, graphical symbology, and interactive legends. Using these visualization functions improves the access and analysis of spatio-temporal data for non-technical users.

The major part of the information of this page is from Rivest, S. et al. [4] and Proulx, M.-J. & Bédard, Y. [6].


Various Display Types (maps, tables, statistical diagrams)

A SOLAP tool supports tabular views and various types of diagrams (horizontal and vertical bar charts, pie charts, point charts, line charts, area charts, etc). Various types of maps can also be built, according to the selections conducted on the different dimensions. Simple maps and multimaps are common. Complex thematic maps and maps with superimposed diagrams are more specialized and allow for the representation of many dimensions on a map or many measures on a map or both. To produce advanced maps instantaneously without SQL operation, built-in rules must exist inside the application.

Simple maps show many geometric elements that reflect a multiple selection on a single spatial dimension. Multimaps reflect the concept of small multiples (i.e. a series of maps, for example a different map per year) introduced by [5], based on the concept of collections by Bertin, [1]. Multimaps are usually used to show a temporal evolution of a phenomenon.
Maps with superimposed diagrams are maps with small histograms or pie charts superimposed on the geometric elements of the spatial dimension (ex. the different regions). This cartographic representation is the result of multiple selections on many dimensions. Complex thematic maps are composed of superimposed visual variables (ex. color, pattern, shape of symbols), one per selected measure. This particular example represents the combinaison of two different measures on the same map, one being represented by colors and the other by patterns.

Synchronisation of operations in the different displays

The SOLAP tool must allow for the synchronization of operations from one display to another. It is important that a selection in one display be effective for all other displays.

This synchronization allows the user to visualize the same information, but from a different perspective: a table for a detailed view of a phenomenon, a diagram for rapid comparisons and a map for the effective visualization of spatial trends or correlations. Temporal comparisons are usually analyzed through diagrams, but the SOLAP tool also offers the possibility to show several maps (called multimaps), diagrams and tables for different epochs, or for different members of the other dimensions, and even to browse rapidly through them to simulate dynamic mapping. A SOLAP operation executed on one display can be, if this type of synchronization is activated by the user, reflected immediately and automatically in all the other displays in the same collection (a collection being a set of linked displays that are synchronized together).

Graphical Semiology Management (ex. classification types, colors)

The symbology that is used to represent the different measures in the various types of display can be defined by the administrator of the system. A SOLAP tool must offer a flexible graphical symbology manager that allows for the definition of different types of data categorization, different types of thematic maps, and the use of various visual variables. The end-users can also create their own personal symbologies to be applied within their own analysis sessions.

However, doing so may lead to potential collisions of graphical symbology rules since the same rules do not always apply to maps, pie charts, bar charts, tables, etc. It is then necessary to keep a visual homogeneity serving as a link from one display to the other and from one navigation operation to the other.

This is even more necessary since the nature of the different types of display (maps, diagrams and tables) affect the quantity and the nature of the information that may be represented by each one.

On a map, a limited number of themes can be represented in order for the map to be visualized as one image and remain readable. There are possible conflicts between the displays and it then becomes necessary to define priorities in the use of visual variables. A graphical rules manager must be implemented into a SOLAP tool to minimize the potential collisions and to easily create multimaps, complex thematic maps and maps with superimposed diagrams respecting state of the art rules.

The synchronization of the graphical symbology from one display to another cognitively facilitates the identification and the interpretation of the data. Using the same symbology in all the displays, it becomes easier to spot and highlight relevant information.

 

Contextual Spatial Data

One of the benefits of using maps is to use contextual information to help users to locate themselves. This contextual information is essential to the analysis in many situations. Different types of information about the area surrounding the studied phenomenon are often as important in constructing knowledge as the phenomenon itself. Within a map display, it is possible to add different types of data (ex. road network, hydrography, administrative limits, aerial photographies) in the background of the map to achieve this goal. A SOLAP tool must thus allow to display contextual data in addition to the spatial data being used for the thematic representation.

 

Interactive legend (allowing drill operations)

Pastor [2] worked at defining elements of interactivity that could be incorporated into the legends of the different displays in a SOLAP interface. The interactive legend can be seen as a graphical view specific to the semantics of the analyzed data. This way, and because SOLAP navigation is allowed in all views (or displays) of data, it is also interesting to define navigation capabilities within the legend to remain consistent throughout the user interface. The interactive legend proposes a new type of SOLAP operation: the classification drill operation that is a drill (down or up) applied on the data classification used to represent measures in the different displays. This operation allows for the visualization of different levels of details of the data classification.


References:

[1] Bertin, J., 1967. Sémiologie graphique: les diagrammes, les réseaux, les cartes. Mouton, Paris.

[2] Pastor, J., 2004. Conception d'une légende interactive et forable pour le SOLAP. Unpublished M.Sc. Thesis, Geomatics Sciences Department, Université Laval. http://www.theses.ulaval.ca/2004/21994/21994.pdf. Accessed October 12, 2005.

[3] Rivest, S., Bédard, Y., Marchand, P., 2001. Towards better support for spatial decision-making: defining the characteristics of Spatial On-Line Analytical Processing (SOLAP). Geomatica, the Journal of the Canadian Institute of Geomatics 55 (4), pp. 539–555.

[4] Rivest, S., Y. Bédard, M.-J. Proulx, M. Nadeau, F. Hubert & J. Pastor, 2005, SOLAP: Merging Business Intelligence with Geospatial Technology for Interactive Spatio-Temporal Exploration and Analysis of Data, Journal of International Society for Photogrammetry and Remote Sensing (ISPRS) "Advances in spatio-temporal analysis and representation", 60 (1), pp. 17-33.

[5] Tufte, E.R., 1983. The Visual Display of Quantitative Information. Graphics Press.

[6] Proulx, M.-J., Y. Bédard, 2008, Fundamental Characteristics of Spatial OLAP Technologies as Selection Criteria, Location Intelligence 2008, April 29, Santa Clara, CA, USA

 

Université Laval - Canada
Updated: November 2009