Introduction to Mapping (Soil Inventory and Evaluation)

1. Introduction to Mapping (Soil Inventory and Evaluation)

2. INTRODUCTION - Concepts of Soil Mapping • Mapping is the grouping of polypedons of one soil series (and similar soils) into landscape units represented by polygons on maps. • The minimum size of the polygon delineation is ¼ inch wide. The area is determined by the mapping scale. • In this class, we will make on-site (called Order 1) soil evaluations or maps. This means we must identify soils to the series level. • We first consult a soil survey if one exists. • Then we cut up the landscape into landform segments (proposed delineations) following the rules of delineation provided, then dig in each proposed delineation to confirm what soil(s) are inside. • We adjust the proposed delineation lines as we dig and transect the mapping area. • We describe and identify the soil at every hole and then produce a map and legend and a report for the map user.

3. Making delineations based on topographic lines and field work: • Never group flooded with non-flooded areas. • Minimum size of a delineation (polygon) is 1/4" diameter if the area is round, but it can be 1/8" wide if it is 1/2 or more long (such as a narrow drainageway or floodplain unit). • Spot symbols are used for smaller areas of important soil or hydrology differences. • Floodplains have 2% slope or less and carry water for longer than 30 minutes after a rain stops. • Drainageways are steeper and runoff disappears within 30 minutes after a heavy rain stops. • Never combine adjacent areas with different slope classes described on page 1. • Separate summits from shoulders, sideslopes from shoulders, and footslopes from sideslopes. • Separate water- collecting from water-shedding landforms.

4. Figure 1a. Topographic map of a survey area before surveying.

5. Fig. 1b. Topographic map with preliminary landscape units and slope classes drawn out.