734 SOILS: PEOFEETIES AND MANAGEMENT 



states use a larger scale, and in reeonnoissance surveys 

 a smaller scale is used- While a large scale increases 

 the detail that may be represented, it also multiplies 

 the difBculties of making an accurate classification 

 because it increases the number of properties to be 

 observed. 



The nature and occurrence of soils in the field involves 

 more variations than can be shown on the map. The 

 boundaries of soil types grade into one another, and it 

 may not be possible to mark the division within several 

 rods. Sometimes even a wider range occurs. The accu- 

 racy with which the boundary may be determined and 

 drawn depends very much on the way in which the two 

 adjacent soils have been formed. If they are very dif- 

 ferent, the boundary may be very distinct. Some types 

 of soil are characterized by local variations in sections, 

 or from point to point, which are on too small a scale to 

 be recognized as a type. Variations may* be induced in a 

 type due to differences in topography, drainage, or culti- 

 vation. Where the properties do not bring about an 

 important change in the crop relations of the soil, they 

 may be ignored. Differences due to cultivation are 

 generally disregarded. The soil survey is made to cover 

 a period of years, and only permanent differences should 

 be considered. 



Variations in the soil must be considered in relation to 

 the scale of the map. On a scale of one inch to a mile 

 the minimum area that can be shown is about ten acres. 

 Occasionally, where the difference in type constitutes a 

 striking contrast, the small area may be somewhat ex- 

 aggerated in size. An area of muck soil having high 

 value for the production of truck crops might be such an 

 exception. 



