A SEAMLESS QUATERNARY GEOLOGY MAP OF SOUTHERN ONTARIO

In response to increased demand for readily accessible and easily understood information on the surficial sediments of southern Ontario, the Ontario Geological Survey (OGS) has undertaken an initiative to generate a GIS based, seamless map of the Quaternary geology for the region.

Over the past 40 years the OGS and Geological Survey of Canada (GSC) have completed Quaternary mapping, primarily at a scale of 1:50 000, for most of southern Ontario. A total of 124 maps, 36 of which belong to the GSC were used to create the seamless coverage. These original, tiled maps existed as digital vector or raster format. The raster images were rubber sheeted to a geographic base and digitized (head’s up) according to the project standards. Polygonal, point and line information was captured as part of the automation process. Attribute tables were built and populated with various geological information.

The original maps contained legends of varying detail and terminology, therefore, a single, standard legend suitable for a 1:50 000 compilation was constructed. This legend created in Access was used to translate all original map units to the new standard legend. Each of the map attribute tables were joined to the translation table using a unique key. A series of additional attributes, for instance, primary material and genesis, amongst others, were extracted from each map sheet and attached to this table. By capturing these attributes a variety of derivative maps can be produced. For instance, a map of gravel resources for aggregate resource assessment studies can be derived from the primary material attribute.

Once all attribute tables were standardized and the translation table completed, coverages were appended together to create a tiled coverage for all of southern Ontario. Boundary faults were found to exist between individual map tiles for most polygons crossing map boundaries. These faults were corrected through field investigations, examination of other geoscience data sets, e.g. aggregate resource papers, and a digital elevation model (DEM) produced by the Ministry of Natural Resources, Ontario and its derivatives.

At present the map is seamless on four attributes, geology, primary material, genesis and formation. Coverages are available on a series of CDs and distribution on the internet is being considered.