5.0 POST-FIELD ACTIVITIES
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5.1 Final Map and Legend Preparation
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The report "A Soil Mapping System for Canada: Revised" (Mapping Systems Working Group, 1981) outlines several different forms of legends and symbols and some of the reasons why they are appropriate for specific uses. The final soil map legend is the culmination of a systematic process where the significant components of the soil landscape are combined into a finite number of soils and soil map units. This synthesis occurs from the start of the soil survey where the descriptions of soils at very many sites are amalgamated or synthesized in a process that reflects the objectives and purpose of the survey.
There are basically four forms of legends:
1. Open Legend
An open legend is, as the name implies, structured so that a map unit is essentially that area for which the symbols are exactly the same. In other words, a change of a class of soil or landscape feature (e.g. slope) creates a new map unit.
An open legend has the following characteristics:
· various soil and landscape properties are assigned (different) letters or numbers.
· each delineation is described by a composite symbol made up of these letters and symbols that are usually connotative.
· the legend contains a definition for the classes of properties.
· most delineations are unique.
An example symbol would be:
2. Uncontrolled Legend
An uncontrolled legend is one where all mapping individuals (soils and non-soils) are listed in the legend (e.g. names, symbols, colour) but the combination of the mapping individuals used to describe a map delineation are not listed or described. Symbols for Phases are usually put in the denominator portion of the symbol and described elsewhere in the legend.
An uncontrolled legend has the following characteristics:
· all recognized soils and non-soils are listed in the legend.
· map delineations are indicated by soil or non-soil symbols.
· various combinations of soils are not listed and described.
An example of a compound map unit would be as follows; note that the user would have to refer to both Soil B and Soil A to gain sufficient information from the legend about this map delineation.
3. Controlled Legend
A controlled legend is similar to an uncontrolled legend with the important exception that all mapping individuals and their combinations are described in the legend. Symbols for Phases such as slope or stoniness are usually put in the denominator portion of the symbol and described elsewhere in the legend.
A controlled legend has the following characteristics:
· all soils and nonsoils, and all their combination are listed and described in the legend.
· soil phases are described in different portions of the legend.
· all delineations with exactly the same map symbol constitute a map unit.
An example symbol would be as follows; note that this compound map unit would be listed in the legend.
This symbol (map unit) would be described in the legend separately from the following symbol:
A2 - B3
3 - 2
4. Closed Legend
A closed legend is one where all combinations of symbols used to describe a map delineation, including phases, are listed and described in the legend.
A closed legend has the following characteristics:
· all combinations of soils, nonsoils and phases, including proportions (where used) are listed and described in the legend.
· all delineations with exactly the same symbol constitute a map unit.
In the example used above for a controlled legend, not only would the symbol B3 - A2 be 3 - 2
listed and described separately from A2 - B3, but so would A2 - B3 as well as B3 - A2.
3 - 2 2 - 3 2 - 3
The preliminary map legend used in the field for mapping purposes is usually an open form since this is the best way to organize and remember facts about the map area when little is known about the relationships among the soils and map units. As work progresses, from inspections (soil pits) to delineations and finally to a soil legend, it changes from a open form to an uncontrolled form. This working legend is useful for the surveyor since the characteristics of the area can be readily displayed by the symbol. However, the publication legend is different in that it is developed for the user who usually wishes to go from a symbol on the map to the legend that describes the symbol and hence the characteristics of the area and this is usually best provided by a closed legend.
An example of an uncontrolled legend is provided in Figure 5.1. The objectives of the soil survey and the user groups will determine the most appropriate legend. For example, it may be appropriate to use an expanded legend format when no soil report is to be prepared for the survey. The expanded legend provides a thorough description of the map unit in terms of definitive and accessory characteristics to aid the user in understanding the landscape relationships of the map unit.
5.2 Map Symbolization and Legibility
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As discussed in section 3.1.7, the minimum size for a map delineation is recommended to be 0.5 cm2 (on the published map). Where there are many delineations on the map which are near the minimum size or the map symbol is so large that many have to be printed outside of the delineation (and "arrowed-in" to the delineation), the map becomes difficult to read. This problem of legibility is often a major cause of soil map users becoming frustrated to the degree that they conclude the soil map cannot be used for their application.
As a guide, it is recommended that the average size delineation (total land area of the map divided by the total number of delineations) be about 20 times bigger than the minimum size delineation (Mapping Systems Working Group, 1981). Based on the following formula, this will result in a map delineation density of 5%. This is a constant regardless of the SIL.
Map Delineation Density = Minimum Size Delineation x 100
Average Size Delineation
The type of map unit symbols used on the soil map are considered to be the choice of the soil surveyor reflecting the needs of the identified user groups. Consequently, it is not reasonable to recommend a specific type of symbol which will meet all circumstances. However, for soil survey maps in B.C. that will be entered into a digital file format, the following type of symbol is recommended, where additional phase symbols can be added as required:
Map legibility must be of concern to the person responsible for preparing the soil map beginning at the project planning stage right through to the publication stage.
5.3 Computer Files and Geographic Information Systems for Maps and Data
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The use of computers and computer software for the purposes of storing soil and map (polygon) data has greatly increased in B.C. over the past few years. The B.C. Soil Information System (BCSIS) has been developed over many years and became operational in 1983. An example of output from BCSIS is illustrated in Figure 5.2. BCSIS contains three types of data: site data; soil data; and laboratory data. The forms provided in Appendix B (and outlined in Describing Ecosystems in the Field - Luttmerding (ed), 1990), provided the means for the surveyor to enter this data into BCSIS. Laboratory data from the analysis of sampled soils is also contained in BCSIS. A parallel data base is available from the federal government and referred to as the Canadian Soil Information System (CanSIS). In addition to this, some soil maps have been digitized. That is, the boundaries of all polygons have been digitized and can be georeferenced through the use of a Geographic Information System (GIS).
Figure 5.1 Example of a Controlled Legend
(taken from soils of the Langley-Vancouver Map Area; Luttmerding, 1980)
Figure 5.2 Example of Computer Output from BCSIS
(from Agriculture Canada, 1980: Soils of the Lac La Hache - Clinton Area, BC)
For all systematic soil surveys, it is recommended that the site, soil and laboratory data be entered into a digital file for the purpose of aiding the mapping effort, to help assure data is not misplaced and to provide a means of referencing the data for comparison purposes. While BCSIS may not be the most appropriate system for this purpose since it is not currently being up-dated and maintained, a data file of similar design could be used. Where applicable, polygon boundaries should be digitized and linked to the data files that contain the attributes of the soil that has been mapped. In addition, it is recommended that, where applicable, existing soil inventories be digitized in an appropriate system, along with all appropriate data.
Geographic Information Systems (GIS) and related technologies have become an essential component for the compilation and use of soils and soils-related data. Valuable information is provided to the soil mapping process since GIS can provide items such as digital elevation models, image processing and integration of multiple data sources. In addition, the spatial analysis capability of GIS is suited for modelling and monitoring soil related phenomena. However, it should be noted that there is an inherent level of accuracy and precision for the soil map and related data which is expressed by the Survey Intensity Level (SIL - see Section 2.2.2). Given that digital mapping can essentially reproduce the map at any scale, it is critical that the user be aware of the SIL for the soil map being utilized. Simply enlarging the soil map does not increase the accuracy or reliability of the information.
The fact that automated soils data (attribute files and polygon files) can be readily integrated with other data sets through polygon overlay is of significant importance to organizations like the Resources Inventory Committee (RIC). Other inventories such as terrain, geology and vegetation can use the same base maps and file structure as the soil survey in order for all of these data sets to be compatible. These tools enable the integration of these data sets to be undertaken with significant cost and time savings.
5.4 The Soil Survey Report
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A soil survey is only partly completed when the soils have been named, described, interpreted, and delineated on a map, and when the laboratory data and other data has been assembled. The mass of detailed information then needs to be organized so it will be readily useful to different groups of users, among them landscape architects, gardeners, science teachers, engineers, planners, developers and builders, homebuyers, foresters, farmers, and those seeking recreation. Presenting the detailed information in an organized, understandable manner is the purpose of a soil survey report. In a practical way, the soil survey report supports the map(s) and enables the user to make greater use of the information. However, the need for a report will depend on the objectives of the survey. The decision whether or not to spend time and budget on its preparation should be decided early in the survey planning stage.
While there are no specific established guidelines for a soil survey report, the data included in the report must always be accurate and scientifically valid. The reports organization and content usually varies with the characteristics of the landscape being mapped, the recognized user groups and the agency or individuals responsible for the survey. Some soil surveys are conducted and maps produced that do not have a supporting soil survey report but rather an expanded legend with supporting data available from other sources (e.g. data files).
At a minimum, the soil survey report should contain the following chapters for it to be considered complete and of the greatest use to the user groups:
1. Index to the Map Units (page reference to the description of the map units).
2. General Description of the Map Area (location of the map area; history and development; climate; physiography and drainage; vegetation; geology and parent materials of the soils).
3. How the Survey was Conducted (outline of methods and techniques used).
4. The Mapped Soils (general descriptions of all soil map units often supported by cross-sectional diagrams).
5. Formation, Morphology and Classification of the Soils (factors of soil formation; morphology of the soils; processes of soil horizon differentiation; landscape relationships among soils).
6. Interpretations, Use and Management of the Soils (capability classification; engineering uses; etc.).
7. Descriptions and Analysis of the Soils (profile descriptions of typical pedons; laboratory data); these can be included in the main body of the report or in an Appendix.
8. Literature Cited
9. Appendices (as required); Soil Map(s) and Legend (bound in report or in map pocket).
5.5 Maintenance and Access of Data Collected
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When a soil survey is undertaken by a government agency or by a consultant paid by a government agency, it is considered public property. The same cannot be said for soil surveys that are undertaken by private organizations. However, it is hoped that these organizations would cooperate in making their information available for the common good of the community.
Regardless of who undertakes the soil survey, they have an obligation to make the accurate information available in a timely manner and to ensure that the data and information is maintained in an easily accessible and up-to-date manner. All data should be archived in an appropriate fashion for future applications.
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