Visualizing Time-Evolving Linked Geospatial Data

Linked geospatial data is receiving growing attention these days, as researchers and users have access to increasingly mature semantic web technology which they can use to publish and structure their data. As well as these tools, new datasets are constantly being produced and existing ones are constantly being updated and extended. We have a rich and growing resource.

While the main focus of research is on publishing and querying these data in an efficient way, humans are not machines and in most cases viewing the text-based results of a query is not enough to fully understand them. This is an especially important consideration when dealing with geospatial data, as the serialization of geometric information for a human is a series of numbers and nothing more and the geometry itself is lost.

Sextant, a new Approach

To deal with this problem we need to implement visualisation techniques that present the outcome of SPARQL queries in a human readable format. Sextant is a web based and mobile ready platform for visualizing, exploring and interacting with linked geospatial data. The old version of Sextant, was one of the first visualization tools for linked geospatial data, but it was focused heavily on the use of SPARQL from the end-user. In the new approach, we re-designed and re-implemented Sextant as part of the MELODIES project, focusing on creating a user-friendly application that would allow both domain experts and non-experts to take advantage of semantic web technologies, and convince them to adopt these technologies by presenting the benefits of the linked open geospatial Web through the use of Sextant.

The core feature of Sextant is the ability to create thematic maps by combining geospatial and temporal information that exists in a number of heterogeneous data sources ranging from standard SPARQL endpoints, to SPARQL endpoints following the standard GeoSPARQL defined by the Open Geospatial Consortium (OGC), or well-adopted geospatial file formats, like KML, GML and GeoTIFF.

A user-friendly Application

The main goal when we started to re-design the application was to build a user-friendly application that would not only cover the needs of domain experts, but also assist non-experts in using semantic web technologies and visualize linked geospatial data. To achieve this goal, we build new smart features in the UI that undertake the construction of SPARQL queries from user input, so that the user is not obliged to learn SPARQL to use the features of the application.

One of the basic features of Sextant, is to provide an interface for querying SPARQL endpoints using stSPARQL or GeoSPARQL and presenting the results as a layer on the world map. In the current version of Sextant, users can use the platform to pose queries to various SPARQL endpoints, such as Strabon endpoints and the Ordnance Survey SPARQL endpoint. This querying feature was originally designed to be used by domain experts or users familiar with these query languages, but we wanted to provide a way for non-experts to use this feature too. To accomplish that we added the predefined queries feature. Predefined queries are a set of queries written by an expert that are made available through an endpoint to non-expert users of the platform.


Another useful feature for understanding the power of linked data is the Explore functionality that allows the visualisation of an ontology stored in a SPARQL endpoint and the discovery of the URIs without the need of writing any SPARQL query.

Demo Map

To grasp the potential of Sextant we have created a demo map with all types of layers, where you can view some of the new features, play with the colorization of the layers, the explore panel and the UI of the application. We are very interested in getting feedback from our users so that we can continue to improve the features and even add new ones to cope with user needs. 

For more information regarding Sextant you can visit our new web site, where you can find links to download the latest version and a complete manual for the application!

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