Selective progressive transmission of vector data

Delivering raw geospatial data to mobile devices is an interesting and challenging computational and user-interface problem. Geospatial data can be rendered in real-time on the mobile device using appropriate visualisation software running on the mobile device operating system. Currently the majority of approaches in delivering geospatial data to mobile devices provide pre-rendered maps (tiles, images). While tile-based approaches have evolved into a defacto standard we feel there are a number of advantages in delivering geospatial data in raw vector formats (XML, GML, Shapefile, etc) to mobile devices including: User personalisation: User can choose which geographical features are displayed, change map themes, set visualisation preferences, etc. Timeliness: The user is always provided with the most up-to-date and recent versions of the spatial data. A number of contraints imposed by the mobile device environment provide major challenges including: screen resolution, available network bandwidth, and usability issues arising from providing map visualisation on small screens (Raper et al.; 2007). In this extended abstract we describe an implementation of a selective progressive transmission scheme for vector data. We use OpenStreetMap (OSM) as the case-study vector dataset. OSM data has a number of attractive features which make it a useful case study, these including: in many areas, OSM data often changes very quickly; OSM attempts to map a very wide range of geographical features; and is freely and openly available. In our implementation a user requests an area of OSM data they wish to view on their mobile device. This OSM data is downloaded immediately on the server where it is generalised. This OSM data package is then progressively transmitted beginning with a low level of detail version of the dataset. In an iterative process additional spatial detail is transmitted to the mobile device until the full resolution dataset is delivered. Our paper provides a brief overview of the implementation of our progressive transmission scheme. We describe an example of selective progressive transmission for a sample OSM dataset.