Abstract:
Cartography is the science and art of making maps and thematic cartography is a subsection that deals with the production of thematic maps. A thematic map portrays the distribution of features, incidents or classifications related to a specific topic. With the rapidly increasing volumes of data, thematic maps allow users to efficiently analyse data and identify trends quicker. A spatial data infrastructure (SDI) focuses on making data available and ensures data interoperability through a geoportal and associated web services for discovery, display, editing, and analysis. Implementations of web service standards by the Open Geospatial Consortium (OGC), and the ISO/TC211, Geographic information/Geomatics enable the display, query and custom visualisation of spatial data in a geoportal. In the past, sophisticated cartographic methods have been mainly available on desktop applications, but with the advances in web mapping technology these methods have become increasingly popular on the Web. Currently, producing thematic maps using web services is a manual process that requires quite a lot of custom programming. The orchestrations of standard web services automate the process to produce thematic maps in a geoportal. It is preferable to use standard web services as opposed to customised programming; the standards provide flexibility, interoperability, and standard protocols, to name a few benefits. The goal of this research was to determine how standard OGC web services could be orchestrated to produce thematic maps within the geoportal of an SDI. To achieve this goal, an orchestrated thematic web service, named ThematicWS, was constructed from existing implementations of individual standard OGC web services, which are monolithic and interchangeable. The thematic cartographic process for producing choropleth and proportional symbol maps was investigated to model the process and obtain a set of steps. Experiments were performed to determine which existing web service standards could be used in the process. ThematicWS was developed using existing implementations of the following standards: WFS to retrieve the attribute data, WPS for the wrapping of custom functionalities (statistical processing and SLD generation), and a WMS to produce the thematic map image. The 52° North and ZOO project frameworks’ orchestration capabilities were evaluated for to determine the suitability for producing thematic maps. The evaluation showed that orchestration is possible in both frameworks. However, there are limitations in both frameworks for automatic orchestration such as the lack of semantic information and poor usability of the framework. The use of WPS services to wrap custom functionalities and to provide a standard interface has proved to be useful for the orchestration of standard web services. ThematicWS was successfully implemented based on standard web service implementations using both workflow scripting and workflow modelling. The orchestrated ThematicWS can be called and consumed by a geoportal of an SDI to produce thematic maps according to user defined parameters.
