Management of spatial data for visualization on mobile devices

Vector-based mapping is emerging as a preferred format in Location-based Services(LBS), because it can deliver an up-to-date and interactive map visualization. The Progressive Transmission(PT) technique has been developed to enable the ecient transmission of vector data over the internet by delivering various incremental levels of detail(LoD). However, it is still challenging to apply this technique in a mobile context due to many inherent limitations of mobile devices, such as small screen size, slow processors and limited memory. Taking account of these limitations, PT has been extended by developing a framework of ecient data management for the visualization of spatial data on mobile devices. A data generalization framework is proposed and implemented in a software application. This application can signicantly reduce the volume of data for transmission and enable quick access to a simplied version of data while preserving appropriate visualization quality. Using volunteered geographic information as a case-study, the framework shows exibility in delivering up-to-date spatial information from dynamic data sources. Three models of PT are designed and implemented to transmit the additional LoD renements: a full scale PT as an inverse of generalisation, a viewdependent PT, and a heuristic optimised view-dependent PT. These models are evaluated with user trials and application examples. The heuristic optimised view-dependent PT has shown a signicant enhancement over the traditional PT in terms of bandwidth-saving and smoothness of transitions. A parallel data management strategy associated with three corresponding algorithms has been developed to handle LoD spatial data on mobile clients. This strategy enables the map rendering to be performed in parallel with a process which retrieves the data for the next map location the user will require. A viewdependent approach has been integrated to monitor the volume of each LoD for visible area. The demonstration of a exible rendering style shows its potential use in visualizing dynamic geoprocessed data. Future work may extend this to integrate topological constraints and semantic constraints for enhancing the vector map visualization

User generated spatial content: an analysis of the phenomenon and its challenges for mapping agencies

Since the World Wide Web (Web) became a medium to serve information, its impact on geographic information has been constantly growing. Today the evolution of the bi-directional Web 2.0 has created the phenomenon of User Generated Spatial Content. In this Thesis the focus is into analysing different aspects of this phenomenon from the perspective of a mapping agency and also developing methodologies for meeting the challenges revealed. In this context two empirical studies are conducted. The first examines the spatial dimension of the popular Web 2.0 photo-sharing websites like Flickr, Panoramio, Picasa Web and Geograph, mainly investigating whether such Web applications can serve as sources of spatial content. The findings show that only Web applications that urge users to interact directly with spatial entities can serve as universal sources of spatial content. The second study looks into data quality issues of the OpenStreetMap, a popular wiki-based Web mapping application. Here the focus is on the positional accuracy and attribution quality of the user generated spatial entities. The research reveals that positional accuracy is fit for a number of purposes. On the other hand, the user contributed attributes suffer from inconsistencies. This is mainly due to the lack of a methodology that could help to the formalisation of the contribution process, and thus enhance the overall quality of the dataset. The Thesis explores a formalisation process through an XML Schema for remedying this problem. Finally, the advantages of using vector data in order to enhance interactivity and thus create more efficient and bi-directional Web 2.0 mapping applications is analysed and a new method for vector data transmission over the Web is presented