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Hydrologic Soli GrouP-Rifle Area, Colorado, Fiarts of Garlleld and Mesa <br />Counties <br />USDA 'm <br />Aggregation is the process by which a set of component attribute values is reduced <br />to a single value that represents the map unit as a whole. <br />A map unit is typically composed of one or more "components". A component is <br />either some type of soil or some nonsoil entity, e.g., rock outcrop. For the attribute <br />being aggregated, the first step of the aggregation process is to derive one attribute <br />value for each of a map unit's components. From this set of component attributes, <br />the next step of the aggregation process derives a single value that represents the <br />map unit as a whole. Once a single value for each map unit is derived, a thematic <br />map for soil map units can be rendered. Aggregation must be done because, on <br />any soil map, map units are delineated but components are not. <br />For each of a map unit's components, a corresponding percent composition is <br />recorded. A percent composition of60 indicates that the corresponding component <br />typically makes up approximately 60% of the map unit. Percent composition is a <br />critical factor in some, but not all, aggregation methods. <br />The aggregation method "Dominant Condition" first groups like attribute values for <br />the components in a map unit. For each group, percent composition is set to the <br />sum of the percent composition of all components participating in thai group. These . <br />groups now represent "conditions" rather than components. The attribute value <br />associated with the group with the highest cumulative percent composition is <br />returned. If more than one group shares the highest cumulative percent <br />composition, the corresponding "tie-break" rule determines which value should be <br />returned. The "tie-break" rule indicates whether the lower or higher group value <br />should be returned in the case of a percent composition tie. <br />The result returned by this aggregation method represents the dominant condition <br />throughout the map unit only when no tie has occurred. <br />Component Percent Cutoff: None Specified <br />Components whose percent composition is below the cutoff value will not be <br />considered. If no cutoff value is specified, all components in the database will be <br />considered. The data for some contrasting soils of minor extent may not be in the <br />database, and therefore are not considered. <br />Tie-break Rule: Lower <br />The tie-break rule indicates which value should be selected from a set of multiple <br />candidate values, or which value should be selected In the event of a percent <br />composition tie. <br />Natural Resources <br />Conservation Service <br />Web Soil survey 2.0 <br />National Cooperatlve Soil Survey <br />RTZ Industrial Site <br />212812008 <br />Page 5 of5