TERRAIN SYMBOLS

Stratigraphic Units
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Many terrain polygons include more than one kind of material, and so the simple terrain symbol commonly must be modified in order to:

Describe map units that include more than one type of terrain (composite symbols).
Provide subsurface information (stratigraphic symbols).
Provide additional information (often project specific) about surficial materials and/or geological processes (subclasses and subtypes).

COMPOSITE SYMBOLS

Areas of uniform terrain are commonly so small that they cannot be delimited individually at the scale of mapping. Consequently, a system of composite symbols is employed whereby up to three types of surficial material may be designated within a terrain unit boundary. A composite unit is made up of two or three simple symbols, each referred to as a component of the composite symbol, with the geological process symbols placed after a dash (hyphen). The components are arranged in decreasing order of areal extent, and are separated by delimiters or deciles. At present, delimiters are used for most mapping. Surficial material that occupies less than 10% of a polygon is generally not indicated in the terrain symbol.

Delimiters

Delimiters indicate the relative amount of each surficial material type represented in a composite symbol. The delimiter symbols are a period sign (^.) and a single or double slash (/, //).

Map Symbol	Definition
^.	components on either side of the symbol are approximately equal in proportion; (see "Terrain Database Manual").
/	the component in front of the symbol is more extensive than the one that follows; can also be used to indicate a discontinuous covering of material, (see Stratigraphic Symbols, Example 3.
//	the component in front of the symbol is considerably more extensive than the component that follows.

Examples of all possible combinations of delimeter symbols and their interpretation follow:

Mb ^. R	Mb and R are roughly equal
Mb/R	R is less than Mb
Mb//R	R is considerably less than Mb
Mb ^. R ^. Cv	Mb, R and Cv are all roughly equal
Mb ^. R/Cv	Mb and R are roughly equal; Cv is less than each of Mb and R
Mb ^. R//Cv	Mb and R are roughly equal; Cv is considerably less than each of Mb and R
Mb/R ^. Cv	R is less than Mb; R and Cv are roughly equal
Mb/R/Cv	R is less than Mb; Cv is less than R
Mb/R//Cv	R is less than Mb; Cv is considerably less than R
Mb//R ^. Cv	Mb is considerably more extensive than each of R and Cv; R and Cv are roughly equal
Mb//R/Cv	R is considerably less than Mb; Cv is less than R
Mb//R//Cv	R is considerably less than Mb; Cv is considerably less than R

Deciles

Where appropriate, e.g., for ecosystem mapping, deciles instead of delimiters may be used to indicate the proportion of each terrain type. The decile, a superscript, immediately precedes the component described. The reliability of the decile estimates should be noted on the map legend and/or report.

Examples:	Mb and Rh each occupy about 50% of the terrain unit area	⁵Mb⁵Rh
	The unit consists of 60% Mb, 30% rock, and 10% colluvium	⁶Mb³R¹Cv

Computer-drafted maps and databases can use regular numbers, e.g., 5Mb5Rh.

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STRATIGRAPHIC SYMBOLS

Stratigraphic symbols are used when two or more kinds of surficial materials are superimposed (Figure 32). They are commonly applied to terrain where the thickness of the surface material is such that the nature of the underlying material(s) may be important, and/or where it is necessary to show the character of the underlying material(s). Superimposed materials are indicated by a vertical alignment of symbols, which are arranged in stratigraphic order, with materials separated by a horizontal line as indicated in the examples below. Surface expression must be indicated for underlying material(s), and texture should be indicated if known. Commonly, only two or three superimposed materials are indicated in this manner. Specific conventions apply to materials draped over bedrock; see surface expression terms: veneer, thin veneer, and mantle of variable thickness. defined as blankets or veneers. Stratigraphic units may be simple terrain symbols or form component(s) of composite terrain symbols.

Figure 32. An example of a stratigraphic unit; sandy gravel beach materials on a gentle slope overlying silty marine sediments (map symbol: ) (location of photo: Vancouver Island).

Examples:	veneer of eolian silt overlying terraced fluvial gravels
	hummocky morainal materials overlying glaciofluvial gravels
	a moderately extensive, but discontinuous, eolian veneer on a river terrace

*Note: The use of a slash in a stratigraphic symbol to indicate a discontinuous layer is new (1997).

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TERRAIN SYMBOLS

STRATIGRAPHIC SYMBOLS

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