Ordnance Survey – Great Britain's national mapping agency
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6.1: Data formats (4)
Open formats
The previous pages in this section have discussed why so many different file types are used in today's GIS applications. Traditionally, data providers have supplied data in open ASCII formats with systems simultaneously loading and translating it into the proprietary binary format. Data can be exchanged between systems where an import option exists for the particular formats. There are also bespoke translation tools available to cover every possible option. Exchange between formats has advanced further in recent years and the term interoperability has become important. Within a single organisation there can be several different software products being used and it is imperative that information can be shared between them.
According to Moore's Law, the processing power of computer hardware can be expected to continue improving. It is therefore becoming less critical to the performance of GIS software for the data to be stored in the optimum format for that particular system. The recent trend for systems to use non-specific data formats means that data is read from, and written to, different native formats on the fly as the software performs its functions.
As a data provider, Ordnance Survey has to make careful decisions about the formats it uses to supply data. Data users want a choice of formats to avoid the need for translation, and although it is difficult to provide every possible format, excluding just one would be unfair to that software vendor. This explains the need for standard open data exchange formats that create a level playing field for the producers of software and translators. The standards being developed by the Open GIS Consortium are becoming a favoured option – see the XML and GML page in the next section.
The increasing significance of databases and the Internet is also playing a big role in the advance of interoperability. Increasingly, systems are being built around the use of databases to hold the information in each GIS layer, replacing the use of flat files. Proprietary binary formats are therefore becoming less important. A similar effect is seen in the way that systems can now read data in real time from central locations on a network, rather than reading from locally stored files. Although this section on data formats set out to highlight differences between file types, these issues will probably have a greater resonance for those practicing GIS in the late 1990s rather than today. There is more to come on spatial databases and the web in forthcoming sections of chapter 6.