SVG explorer of GML data

The OpenGIS Consortium has been developing, through time, the GML (Geography Markup Language) , a non-proprietary language (public domain) specifically defined to codify, archive and transfer (via Internet too) spatial data. Based on the XML standard, the GML handles both the geometry and the properties of the geographical elements; this allows the various data providers to share heterogeneous data sets and the users to access the data in a completely transparent way. From the application point of view, it simplifies and standardizes the operations in many sectors, from map building to data format transformation, from spatial query to geographical analysis, including the emerging applications in mobile systems. Since the GML data structure is XML-compliant, it can be transformed in a SVG (Scalable Vector Graphics) document format and then easily displayed on standard web browser. Because this technology is continuously evolving, this work presents an overview on some aspects of the state-of- the-art, an evaluation of the advantages and disadvantages, and a demo application of the use of this technology in the field of building and querying thematic maps. The SVG Explorer application is running on a web browser (Microsoft Explorer) and all the functionalities are working at the client side on local and/or remote (WWW Internet) data. The application's main goal is the processing of GML documents and their visualization in a graphical way, with the interaction of the user. A set of basic functionalities handling both the graphical (zoom, pan, symbols, styles, ...), the geographical and the thematic aspects (multilayer organization, elements classification and aggregation by attributes, ...) have been developed. SVG is mainly oriented to vector data but can define also raster data as JPEG, PNG files containing georeferenced images; with this approach the overlay of vector data on a raster data background is allowed. All the functionalities are operating in an ECMA Script environment, making use of libraries implementing base primitives working on GML and SVG data structures (as recommended by W3C). The aim of this work is not only building a specific application, but is for three-fold: to validate the XML (GML and SVG in particular) technology in order to verify its capabilities to solve some GIS problems; to migrate the GIS operations from Server to Client side in order to discover which kind of operation can be allowed; to create a basic environment on which develop customized applications integrating a set of specific functions. The SVG Explorer can also be seen as an evolved application using the Web Feature Service (defined by the OpenGIS project) for the features (GML coded) presentation and manipulation at client side.