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Downloading of data

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A key outcome of Spatial Data Infrastructures (SDI) is that geospatial data become more easily accessed. It is important to understand the traditional workflow involved in using geospatial data in order to appreciate why this outcome offers considerable efficiencies.

A GIS user or business system traditionally receives geospatial data as a file on a DVD or other media. In order to use any of that geospatial data, the whole file has to be loaded onto the user’s system. One of the characteristics of spatial information is that it tends to be voluminous so this could involve the transfer of several Gigabytes of data. Moreover, the data may have to be translated from the supplier’s format into a format understood by the user’s system. This can be a time-consuming, processor-hungry activity.

From this, it can be seen that a file download (using a mechanism such as file transfer protocol) offers little advantage over DVD delivery. Indeed, from an ICT perspective, the surge in bandwidth required to download whole files of geospatial information can be seen as a significant disadvantage.

Using a current web services approach, the GIS user or business system can directly connect to the service and thus directly consume the content into their system. This offers a number of advantages. Perhaps most important is that there is no precursor to using the data which offers the opportunity for the GIS or business system to be used more directly as a tool; the effectiveness is improved. In systems terms, the user is able to access just the extent of data required to conduct their task. This reduces processing and bandwidth terms; the efficiency is improved.

The Open Geospatial Organization (OGC) has worked for many years to establish a range of open standards for the web service delivery of spatial content. A wide range of rich standards are available for use.

In particular, the OGC Web Map Service (WMS) defines an interface that allows a client to retrieve maps of georeferenced data. The OGC Web Feature Service (WFS) is the standard service which allow to download vector data from any standard Web Map Server, while OGC Web Coverage Service (WCS) is the preferred standard service to deliver raster data. Environmental analysis are usually performed using raster data (e.g. Salinity, Temperatures, and even Habitats or Land cover layers are usually preferred in raster format for analysis purposes.