The type of line that is used provides valuable information about terrain characteristics and the reliability of polygon boundary locations.
Minimum Requirements: Three types of polygon boundary lines shall be used:
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The letter symbols that are assigned to each terrain polygon represent four or more classes of information. Standard symbols represent:
Mappers should refer to the terrain classification system manual (Howes and Kenk, 1988) for definitions of letter symbols and guidelines for their use. For some projects, soil moisture and slope gradient are also shown on a terrain map (see example in Fig. 1). This additional information is required, for example, on terrain maps that are used as a basis for biophysical mapping and on those that are used for interpretations of slope stability (see example in Section 10.2).
Minimum Requirements: (from Howes and Kenk, 1988)
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Description of a terrain polygon by means of a letter symbol requires not only adherence to the minimum requirements listed above, but also judgment by the mapper. In general, the number of letters used should be as small as is reasonable. Maps covered with long, complicated symbols have been justifiably criticized and then ignored by many potential users!
There are several ways of reducing the length of symbols, for examples:
If the symbol "U" (undifferentiated materials) is used, it should be precisely defined. It should not be used to express the uncertainty of the mapper regarding type of material, but only where several types of material occur within a very small area, as specified by Howes and Kenk (1988). Extensive use of "U", or lack of a specific definition of "U" for a particular map area, hinders the preparation of derivative maps.
Where project objectives require mapping of data that are not normally shown on a terrain map, additional descriptors can be incorporated into the terrain symbol. For example, numerical superscripts have been used with "M" (till) to indicate tills of different lithological composition (e.g., Ryder, 1985); superscripts have been added to the process symbol "-Q" (land subject to flooding) to indicate flood frequencies (Miles and Harding, 1980; Fig. 3); the use of both superscripts and subscripts was suggested by Maynard (1989) to describe the pattern and gradients of gullies for detailed assessment of debris-torrent potential. It is best to use such add-ons for large scale mapping (>1:20,000) and for mapping for specific purposes such as hazard assessment.
On-site symbols are added to terrain maps to indicate specific features that cannot be adequately delimited by the use of terrain polygons and letter symbols. Some of these represent features that are too small or too narrow to be represented by a polygon, such as kettles and terrace scarps; others represent features of relevance to glacial history, such as striations, strandlines, drumlins and cirques. Various mass movement features, such as landslides headscarps and debris flow tracks, also can be shown by on-site symbols.
Mappers should make sure that on-site symbols are clearly depicted on a terrain map, that linear symbols are distinguished from polygon boundary lines, and that on-site symbols do not cause the map to appear unduly cluttered. The appearance of a map can be improved by the use of a grey tone or colour for on-site symbols. In special cases, the problem of clutter may be resolved by the preparation of a separate "terrain features" map that shows only the on-site symbols (Figs. 4 and 5). The preparation of terrain features map is appropriate where on-site symbols provide important information about the location of potential hazards, such as debris flow tracks and avalanche tracks. Maps showing features, such as ice-flow directions, cirques and eskers are a useful tool for reconstruction of glacial history.
The symbols used in terrain mapping must be compatible with digital data storage; and the symbols should be suitable for hand and electronic drafting. The format for presentation adopted here follows the example established by the Bedrock Geology Task Group (RIC, 1995).
The features and symbols were compiled following a priority system. The first document used in the compilation, was Howes and Kenk (1988). Additional references used to flush out the original list included EMR Canada (n.d.), Geological Society of London (1972), Cooke and Doornkamp (1974), Blackadar et a/. (1979), International Association of Engineering Geology (1981a, 1981b), Australian Bureau of Mineral Resources (1989), Grant and Newell (1992) and RIC (1995). Some of the symbols in these references were modified for this compilation. Where no symbol existed, or was found for a specific feature, a symbol was created for this compilation.
The features and symbols have been organized into eight broad categories. These are, in alphabetical order:
The features and symbols within each broad category are also listed alphabetically. Table 5 is a summary of all features for which symbols have been compiled. The compilation of features and symbols is presented in Appendix I. A blank symbol template, with an explanation of each field is presented in Table 6. For the present document, the cartographic definitions and feature codes of the symbols have not been included. As for the bedrock symbol compilation, the terrain and surficial geology symbols were developed for 1:20,000 scale maps. Should this map scale change, the positional definition would change accordingly. The definitions of the features have been gleaned from a number of sources. Some of the definitions abstracted from the bedrock symbol library have been modified to include both rock and soil.
Large scale maps (e.g., 1:20,000) are commonly assumed to be more reliable than small scale maps, and large scale mapping is generally considered to involve more ground checking than small scale mapping. Terms such as "reliability" are hard to define however (although see Section 12.0), and does "more ground checking" mean more time per unit area on the ground or on the map? In its simplest form, terrain mapping can be completed by air photo interpretation, with no ground checking. Specification of survey intensity levels is one approach to the definition of map reliability.
Survey intensity level expresses the relation between map scale and amount of field checking. Six survey intensity levels are used for terrain mapping ("terrain survey intensity levels" or TSIL) are defined in Table 7.
The commonly used definitions of survey intensity (% of polygons field checked) are indicated in column 3. However, the number of field checks per unit area (column 4) can be used as an alternative way of specifying the amount of field checking. For example, where the nature of the landscape results in delimitation of large polygons, it may be preferable to specify survey intensity in terms of checks per unit area rather than by % of polygons. Also, specification of the number of checks per unit area provides a simple way of calculating total number of field checks required. The two methods (columns 3 and 4) can be used concurrently by indicating that field work requires, for example, either xx% of the polygons checked or at least I check per xx ha, whichever results in the greater number of checks.
The definitions of survey intensity levels that are given here differ in two ways from those used by pedologists (c.f., Mapping System Working Group, 1981). First, there is a lesser relation between map scale and survey intensity, and second, the terrain system requires less field checking. For example, in the pedological system, 1:20,000 scale mapping can only be done at SIL 2, whereas in the terrain system, it can be done at TSIL A or B or C. For pedological SlLs 1, 2 and 3, 100%, 90%, and 60-80% of polygons must be checked, whereas checking of 75--100%, 50-75%, and 25-50% of polygons is required for TSILs A, B and C.
For terrain mapping, it is appropriate to have a more flexible relation than in soils mapping between map scale and survey intensity because, under certain circumstances, satisfactory terrain mapping can be done largely or even wholly from air photo interpretation (see TSIL E). Some landforms and hence materials can be reliably recognized on air photos, for example alluvial fans, river terraces, and talus slopes. There is no point in requiring a mapper to field check terrain that has been correctly mapped under the stereoscope, unless project objectives call for additional information, for example, texture. Conversely, air photo interpretation may be hindered by vegetation cover, requiring more ground checking than for similar terrain under sparse vegetation. Thus an appropriate TSIL should be specified for a project according to terrain and vegetation characteristics and not based solely on map scale.
Minimum Requirements:
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