June 2013    Print this article

Notions of integrity in geological compilation

Ghislain Roy
Ministère des Ressources naturelles

It was in the early 1990s that the first geological maps were compiled in the Sigeom geomining information system. At the time, the aim was to provide digital geological coverage of the province by integrating, into one central database, all geology work carried out since the middle of the 19th century. The geological knowledge was gathered from a variety of documents, such as geological reports and graduate theses.

From visualizing to structuring

In the beginning, the goal of geological data compilation using Sigeom was digital cartography and the focus was mainly on data visualization, such as traditional paper maps. The system could tolerate errors introduced during the digitization process if they did not influence the cartographic representation. Representations at different scales or using different perception levels could even conceal some errors of a structural nature. Besides, at the time, Sigeom was held back more by visualization issues than by data structuring problems.

With the arrival of geographic information systems (GIS) and data processing, analytical operations and reasoning rapidly dethroned visualization as the main functionality. These processes exploit all aspects of spatial information, including the shape and location of the objects as well as their attributes. Contrary to visualization, analytical and processing operations are directly affected by errors since the results can be used by decision-support systems. Quality controls based solely on visual features are no longer sufficient because this approach only results in the elimination of errors detectable by the naked eye. Moreover, apparent consistency in cartographic representation does not necessarily guarantee consistency in the source database. For example, a geological zone represented by a closed region (polygon) on a map may not be so in the database. Furthermore, errors do not all have the same repercussions on spatial operations. Some may simply prevent a result from being obtained, whereas others may lead to inconsistent results during more complex operations. The quality of the data (in both spatial and descriptive terms) is therefore a major consideration for any organization using geographic information systems, and Sigeom is no exception.

Towards data integrity

In 2010, Sigeom underwent a major shift as GIS technologies became established in the production of geological data, and earlier tools, such as MicroStation, were abandoned. The transformation revealed numerous problems in the database. In early 2011, a data validation project was set up to conduct a complete review of the geological coverage, both in terms of geological entities and attribute tables. At the same time, all aspects of the production and update processes were reviewed and modified in order to introduce notions of integrity. This undertaking, which will affect the entire set of geological data compiled over the past 20 years, should be completed by early 2014.

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