UKOLN AHDS QA for GIS Interoperability


Quality assurance is essential to ensure GIS (Geographic Information System) data is accurate and can be manipulated easily. To ensure data is interoperable, the designer should audit the GIS records and check them for incompatibilities and errors.

Ensure Content Is Available In An Appropriate GIS Standard

Interoperability between GIS standards is encouraged, enabling complex data types to be compared in unexpected methods. However, the varying standards can limit the potential uses of the data. Designers are often limited by the formats available in different tools. When possible, it is advisable to use OpenGIS - an open, multi-subject standard constructed by an international standard consortium.

Resolve Differences In The Data Structures

To integrate data from multiple databases, the data must be stored in a compatible field structure. Complementary fields in the source and target databases must be of a compatible type (Integer, Floating Point, Date, a Character field of an appropriate length etc.) to avoid the loss of data during the integration process. Checks should also be made that specific fields that are incompatible with similar products (e.g. dBase memo fields) are exported correctly. Specialist advice should be taken to ensure the memo information is not lost.

Ensure Data Meet The Required Standards

Databases are often created in an ad hoc manner without consideration of later requirements. To improve interoperability the designer should ensure data complies with relevant standards. Examples include the BS7666 standard for British postal addresses and the RCHME Thesauri of Architectural Types, Monument Types, and Building Materials.

Compensate For Different Measurement Systems

The merging of two different data sources is likely to present specific problems. When combining two GIS tables, the designer should consider the possibility that they have been constructed using different projection measurement systems (a method of representing the Earth's three-dimensional form on a two-dimensional plane and locate landmarks by a set of co-ordinates). The projection co-ordinate systems vary across nations and through time: the US has five primary co-ordinate systems in use that significantly differ with each other. The British National Grid removes this confusion by using a single co-ordinate, but can cause problems when merging contemporary with pre-1940 maps that were based upon Cassini projection. This may produce incompatibilities and unexpected results when plotted, such as moving boundaries and landmarks to different locations that will need to be rectified before any real benefits can be gained. The designer should understand the project system used for each layer to compensate for inaccuracies.

Ensure Precise Measurements Are Accurate

When recreating real-world objects created by two different people, the designer should note the degree of accuracy. One person may measure to the nearest millimetre, while the other measures to the centimetre. To check this, the designer should answer the following questions:

  1. How many numbers are shown after the point (e.g. 2:12 cm)?
  2. Is this figure consistent with the second designers' measurement methods?
  3. Has the value been rounded up or down, or has a third figure been removed?

These subtle differences may influence the resulting model, particularly when designing smaller objects.

Further Information