44 BULLETIN 696, U. S. DEPARTMENT OF AGRICULTURE. 
Specific application of the maps and tables of this publication 
should take cognizance of the characteristics of the data. Counties 
are the units of measurement, and the figures represent customary 
conditions as determined by a five-year average. Prices reflect 
dynamic conditions. However, an unusual harvest or a market con- 
dition upsetting the ordinary course of business in a given product, 
will also disturb the price zones. 
The normal price ratios, too, are slowly changing, in accord with 
economic conditions, of which they constitute an index. A review 
of price factors from 1871 to 1915 serves to indicate the present 
trend. While the United States average farm price of corn has 
risen, the geographic differences have been approximately cut in two, 
coinciding with decreasing transportation and marketing costs. In 
relation to the general average, the prices in corn-exporting States 
have risen rapidly and steadily; in corn-deficiency States the ratio 
has dropped even more notably. In some cases, notwithstanding 
the general rise in price levels, specific sections show declining prices 
as well as price percentages. 
Corn and wheat prices are rapidly drawing closer. A 60-cent dis- 
parity in 1871-1875 has dwindled to 20 cents in 1911-1915. On the 
other hand, price disparity between corn and oats has widened be- 
cause of the more rapid rise of corn prices. 
The ramifications of price factors involve the entire economic 
structure. The charting of concrete geographic differences has pos- 
sibilities of practical use. Presentation of only a few of the general 
bearings of the price conditions has been attempted here, for it has 
been manifestly impossible in this inquiry to enter into specific local 
surveys. It is also evident that no one factor determines the price 
zones, but each more or less determinate element is affected by others. 
