Mapping And Classification Of The Data

Our database consists of sedimentologic and geomorphic information. Data are compiled in a pseudo-raster format with each cell dimension consisting of 7.5 minutes of latitude by 7.5 minutes of longitude (Fig. 6.3). The study area is divided into 18 zones (each 4 by 6 degrees). Each zone is represented with a grid of 1536 cells (Fig. 6.3). Some zones contain less than this number of cells because they border Canada or the ocean. In each zone, cells are represented by vector polygons, and each is linked to an attribute table, which lists the features found in that cell. For example if drumlins are present in a given 7.5' X 7.5' area the attribute table notes this with the integer '1' in that attribute column for that cell. If drumlins are not located in this area then a '0' is entered. In other attribute columns the type of sediment that lies at the centre of that cell is recorded by an integer value. By this method the presence or absence of glacial features can be recorded, or the type of sediment, sediment thickness or other attribute of the area can be entered into the database.

To create our current maps we used nine attributes for which we have complete coverage (Fig. 6.4). These nine attributes are used as input to create the landsystem maps. From these nine attributes we defined seven different landsystems. Figure 6.5 illustrates how the nine attributes were used to create the seven landsystems shown in Figure 6.6. Some landforms are considered more important than others in this classification scheme. This is the case for features that we

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Figure 6.3 The structure of our geologic database. A) Grid of 1536 cells. We used part of 18 of these grids to cover the study area. B) A close-up of the numbering of the cells that are highlighted in black in A. Each cell is numbered and linked to a database table shown in D. C) An example of a map showing the distribution of sediment types in each cell. D) An attribute table showing the feature attributes for each cell. Though we only show seven attributes here, the database contains more than two dozen attributes for each cell area.

believe are the defining characteristic of a landsystem such as drumlins, till plains with thick glacial sediment, and low-relief hummocky plains. For example, any cell in which drumlins occur is classified as landsystem B (see Fig. 6.6a). Many cells contain landforms and sediments of more than one landsystem because landsystems created during deglaciation were superimposed upon LGM landsystems or because the size of each cell encompasses two or more distinct areas. Nevertheless, our maps show the regional-scale distribution of the dominant landsystems.

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