Land System Database User’s Manual – Methodology

Overview

The land system product is the result of input from many people. It has evolved through a multi-step process.

The CAESA-SIP Procedures Manual describes in detail the rationale and procedure followed during the creation of the preliminary land systems product. In this section, the subsequent correlation (or refinement) of the digital land system delineations and creation of the accompanying legend database is explained.

The following is a summary of the initial development of the land-systems database files included in AGRASID.

Initial development phase

Making working copies

Block leaders of CAESA-SIP created working copy land system maps and accompanying individual descriptions. They used the top-down approach to stratify Alberta’s agricultural region into land systems. Labeling each with a symbol consisting of Ecoregion, Ecodistrict and land-system number.

Creating a database

The block leaders compiled a database describing the preliminary land systems. It contained specific information such as:

• symbol
• landscape descriptors
• surficial materials
• expected soil types

In addition, each land system received a geographic name and morphological descriptor (for example, Ensign Upland).

Soil landscape polygons

Soil analysts delineated and described the attributes of each 1:100K soil landscape polygon. They also assigned each polygon to a specific land system based upon the preliminary land system maps as compiled by the block leader. The analyst incorporated some modifications to that preliminary information.

This meant the updated land system map varied from the preliminary version.

Correlating information

Next, the Land Systems Working Group correlated the land system delineations and developed a legend database.

The land system products included on AGRASID are the result of the following correlation and ‘roll-up’ activities.

Correlation of the land system delineations with the ecological framework etc. was the first step. Then, summarization and organization of the attributes for each soil landscape polygon, similar to a legend followed.

The next 2 sections outline the procedure for compiling these components of the land system data. They also explain the correlation and compilation of the land system legend.

Correlating delineations

The land system maps derived from the pre-release version of the AGRASID files often varied from the original preliminary land system maps, prepared by the block leaders. In addition, the associated land system database required modification.

Land system correlation involved comparing the digital land-systems map with the preliminary version of the map. During this correlation step, the factors under consideration involved:

• Modifying the boundaries of the land system (determined by the allocation of AGRASID soil landscape polygons). This nests the land systems within nationally recognized Ecoregions and Ecodistricts. It also nests them in provincial-scale Soil Correlation Areas (SCAs).
• Evaluating and justifying the uniqueness of neighbouring land systems within Ecodistricts based on soil types and landscape models.
• Amalgamating land system polygons that do not meet the minimum size criteria or 1 township. Lands systems smaller than 1 township were amalgamated with their most similar neighbouring land system.
• Reviewing the allocation of river land systems to Ecoregions. Land systems consisting of a major river (such as the North Saskatchewan River) are unique to Ecoregions (but not Ecodistricts), with respect to their LS_SYM designation.

Modifying the alignment of land systems within AGRASID meant changes to the corresponding files. For example, amalgamating a land system with its neighbour required changing a soil polygon’s LS_SYM. Sometimes the corresponding Ecoregion, Ecodistrict and LS number fields also needed to be changed.

Compiling the legend database

Compilation of the land systems legend database was a 2-step process:

• Determining and reaching agreement on the database structure
• Populating this structure with data.

The following sections describe the generation of the following the tables:

1. The land system legend table: AGRASID41_LandSystemLegend associated with the AGRASID land system spatial data (Appendix 2, Table 2), bundled with the Agriculture Regions of Alberta Soil Inventory Database version 4.1 (AGRASID) for land systems download.
2. The AGRASID 4.1 soil landscape polygons to AGRASID 41 land system legend database relationship table: ag41sl2ag41lslg describes how AGRASID soil landscapes are grouped according to AGRASID41 land systems (Appendix 1 Table 2), bundled with the Agriculture Regions of Alberta Soil Inventory Database version 4.1 (AGRASID) for land systems download.
3. The general land system descriptions:-The AGRASID41_LandSystemGeneral (Appendix 2 Table 5.) bundled with the Agriculture Regions of Alberta Soil Inventory Database version 4.1 (AGRASID) for land systems download and published at open Alberta publication: General land systems descriptions for the agricultural regions of Alberta.

Structuring the legend database

Many people worked on developing the AGRASID_LandSystemLegend table, primarily the Land Systems Working Group. The contents of the legend table consisted of the fields within the preliminary land-systems table initially provided by the block leaders.

This preliminary land system database initially drew on pre - existing soil and landscape information as a starting point, not the AGRASID 1:100K soil landscape polygons and accompanying descriptions because AGRASID soil landscapes did not exist in their finished form at the time. Rather preliminary land systems guided the development of more detailed AGRASID soil landscapes spatial and attribute information. Upon completion of the finalized AGRASID soil landscapes, attribute information a process of summarization and generalization resulted in the land system, legend table included in the initial release of AGRASID.

The working group reviewed:

• Content from pre-existing land systems, map legends and solicited comments from land systems, map users, and.
• Reached agreement on the fields contained within the AGRASID_LandSystemLegend table.

A list and description of the fields in the AGRASID_LandSystemLegend table are located in Appendix 2 table 2.

Populating the legend database file

Assembling the land systems legend database initially involved the development of a procedure to ‘roll up’ the soil and landscape attributes within the other AGRASID files.

This procedure was a multi-stepped process.

Creating tables

The working group used the AGRASID files to determine the areal extent of each soil landscape symbol (MUNAME) within each land system. They specifically used the ag41sl2ag41lslg table joined to the AGRASID_SoilLandscapes polygons, and in turn linked to the PolygonComponents, SoilProfiles, and SoilNames tables. The result was a virtual database table for each land system listing the soil landscape symbols (MUNAME) and a percentage (%) occupied by that soil landscape polygon.

Determining soil names

The team then summarized this virtual table by land system, percent and shape area to determine the proportion of area a soil name occupies in a land system and then determined the major and minor soil names for each land system.

In the SoilNames table a dominant or up to 3 co-dominant soils were identified. Up to 4 significant soils may also be listed. By definition, a dominant soil occupies more than 60% (or a proportion of 0.6 out of 1) of the polygon. A co-dominant soil occupies more than 30% (or 0.3) and less than 60% (0.6) of the polygon. Significant soils occupy more than 10% (or 0.1) and less than 30% (or 0.3).

Based on the definitions for dominant, co-dominant, and significant soils, the following proportion assignments to each soil name using the following values for the areal extent definition took place:

• dominant soils = 0.6
• co-dominant soils = 0.3
• significant soils = 0.1

The group needed to acquire a listing of all individual soil names that occur in a land system. They also needed a relative percentage of the land system each soil occupies. To get this, they multiplied areal extent values of each soil landscape polygon with the areal extent values for each soil name.

For example, if a soil landscape polygon occupies 50% of a land system, a soil name is dominant. This means the soil occupies 30% (50% times 0.6 equals 30%) of the land system.

Deriving other attributes

Based on this list of soil names within each land system, derivation of other soil attributes became possible. These other attributes include:

• soil order
• parent material type and texture
• combinations of classification and parent material

Determining fields

Using these soil attribute tables for each specific land system, the major and minor soil fields were determined and entered within the land system legend table (AGRASID_LandSystemLegend).

This exercise was a manual endeavour since some judgment calls were required. In some cases, the first few values in the summary tables were not automatically the values entered into the major soil field.

For example, with respect to the major and minor soils, the identified soil names were not necessarily the first 5 soil names. Evaluation of representative soil names followed from the ranking of importance of:

• soil order
• subgroup plus parent material, and
• soil name

Accessory fields

The landscape models (LCODE and LMOD) listed in the AGRASID_SoilLandscapes polygons underwent summarization by land system. Generally, the principal features (i.e. hummocky versus inclined or undulating) came under consideration when populating the landscape fields in the AGRASID_LandSystemLegend table.

Creating the general description

The AGRASID_LandSystemLegend table with its coded attribute descriptions is primarily suited for GIS and database applications. The adobe reader document General land systems descriptions for the agricultural regions of Alberta provides users preferring a simplified explanation with a generalized text description of each land systems in a published format.

In addition, the essential components of the general land systems descriptions are now available in both a Microsoft Excel spreadsheet format capable of joining to the ArcGIS formatted land systems shape layer, and an ArcGIS file geodatabase table contained within the AGRASID 4.1 download. A description of the data within this GIS formatted table is contained in Appendix 2, table 3 and the entity relations is illustrated in figure 1 of the features section of this manual.

The text expressions within the general land systems descriptions originate directly from the AGRASID_LandSystemLegend table. They employ the coded data and lookup tables to generate the text expressions for each land system polygons. The following steps describe how the team constructed the text descriptions.

Devising look-up tables

Creation of a series of look-up tables that convert the domain codes within the land system database to standard strings of human readable text was the first step. In some cases, this was a 1-to-1 relationship between a specific code domain and the corresponding standardized strings. In other cases, amalgamations of code domains occurred resulting in fewer classes to describe land system attributes.

For example, 66 landscape models used in AGRASID to describe landscapes at a scale of 1:100,000 simplified to 26 representative landscape descriptions in the land systems dataset.

Use of these look-up tables and those for other soil components such as Soil Zone, Soil Order and Parent Material Texture provided the content for compiling the general land systems descriptions for the agricultural regions of Alberta.

The conversion tables for these various components are available in Appendix 3, Tables 1 to 5.

Describing landscape

Landscape is the first attribute described in the general land system description. The landscape attribute may have from 1 to 3 separate surface forms defined in the AGRASID_LandSystemLegend table.

Describing representative soils

Representative soils description within each land system result from descriptions of soil zone, order and parent material.

Describing combined attributes

Many land systems have more than 1 surface form and/or multiple soils identified in the AGRASID_LandSystemLegend table. These various combinations of attributes are accommodated by adding phrases such as “and” or “with some.”

Here is an example:

• “Landscape is hummocky with some peatlands. Dark Gray Luvisols and organics developed on very fine-textured water-laid sediments and sphagnum peat.”

Major and minor soil order

Minor soils that are distinctly different from the identified major soils are included in the general description.

Sometimes the order of a minor soil is different from that of the major soil. In those cases, a further statement may refer to this difference in soil order between major and minor soil as the example demonstrates:

• “Minor soils include Regosols.”

Major and minor soil texture

Sometimes the texture of a minor soil is strongly contrasting. It may be coarser, finer or more gravelly than the major soils. In those cases, the following are examples of possible additions or appending words or phrases:

• “Minor soils include coarse textured soils.”
• “Minor soils include Regosols and coarse textured soils.”

Eroded soils

Comparisons of each major and minor soil to the list of eroded soils (Appendix 3, Table 5) takes place. If a soil symbol matches 1 of the symbols in Table 5, then addition of the following statement is occurs:

• “Significant eroded soils present”

Putting it all together

The combination of these statements provides a template for the final text description:

“Landscape is landscape. Soil zone and soil order of major soil developed on parent material texture of major soil. Minor soils include soil order of minor soil and coarse textured soil. Eroded soils identified.”

Using the examples in the steps above, a general text description takes shape for a land system:

“Landscape is hummocky. Brown chernozems developed on medium textured till. Minor soils include Regosols and coarse textured soils. Significant eroded soils present.”