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Range Production (Normal Year)-Logan County, Colorado <br />Exhibit J (c) <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 of 60 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 "Weighted Average" computes a weighted average value <br />for all components in the map unit. Percent composition is the weighting factor. <br />The result returned by this aggregation method represents a weighted average <br />value of the corresponding attribute throughout the map unit. <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: Higher <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 />Interpret Nulls as Zero: Yes <br />This option indicates if a null value for a component should be converted to zero <br />before aggregation occurs. This will be done only if a map unit has at least one <br />component where this value is not null. <br />Natural Resources Web Soil Survey 2.1 2/17/2009 <br />Conservation Service National Cooperative Soil Survey Page 4 of 4