For presentation purposes, terrain map data are usually superimposed onto a topographic base map (NTS maps and TRIM maps). The contours on these maps provide information about the large topographic features (mountains, valleys) that are not shown by terrain symbols, relief and slope grade. Terrain information is normally drafted onto 50°/O screened mylar (i.e., a reproducible medium) copies of topographic maps (e.g., Fig. 1). Blackline prints from the mylar map show base map information (contours, cultural features) in grey and terrain information in black.
Topographic maps that are used as base maps should not be enlarged to the presentation scale unless no larger scale map base is available. In practice, 1:50,000 maps have commonly been enlarged to 1:20,000 scale because, until the advent of 1:20,000 scale TRIM mapping in 1990, large scale topographic maps were available only for a few parts of British Columbia. The contour patterns on enlarged topographic maps do not show the small topographic features that are clearly visible on larger scale air photos. Consequently, features shown on the terrain map, such as slope steepness, may be at odds with the contours.
Air photo mosaics and orthophotos can also be used as base maps for terrain mapping. Many people who are not familiar with topographic maps can relate more easily to a photographic base, and so this is a useful option for certain projects. If project objectives specify that an air photo mosaic (or other non-topographic medium) is to be used as a base, then the mapper should show slope steepness on the terrain map, either by using additional descriptors for slope or by using surface expression symbols that specify slope (e.g., "Mv over Ra" rather than Mv alone) in all polygons.
For some projects, terrain maps are prepared on transparent overlays to topographic maps, orthophotos, or other types of map. A terrain overlay is commonly one of a series of thematic overlays that show various types of information that are to be integrated for planning or management purposes. If project objectives require that maps are scanned and digitized, then an overlay showing polygon boundaries only should be made of the map before terrain symbols are added.
Minimum Requirements: Terrain maps shall show:
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It is recommended that a tailored legend (Fig. 10) be prepared for each mapping project. The legend may be specific to one or several map sheets. The smallest letters in the legend should be clearly legible, and on-site symbols should be represented in the legend at approximately the same size as they appear on the map. The legend should appear adjacent to the terrain map, not on the back of the map sheet.
Minimum requirements:
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Information that should be shown in the border of a terrain map is listed in Table 13. If terrain information has been added to an NTS or TRIM map, then some of this information, such as scale, will be present automatically. If terrain mapping is presented on an orthophoto or an overlay, then all information listed as a minimum requirement should be added.
In general, the terrain map and marginal information together should cover an area of no more than one square metre. Large maps should be split into two or more sheets, each with a legend. An example of map layout, with marginal information, is provided in Figure 11.
Terrain maps should be used at the scale at which they were originally presented. They should not be enlarged because this magnifies any errors that are present. Also, since larger-scale maps are commonly thought to be more reliable than smaller scale maps, enlargement can give a misleading impression of accuracy.
Minimum Requirement:
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