Abstract A yield map can be an important tool in guiding the variable rate application of inputsand in assessing the affects that variable rate input application can have on crop yields fora farm field. This paper identifies and examines several factors which determine the qualityof a yield map.Introduction Precision farming (variable rate input application) is based on the premise that auniform application of inputs ( including fertilizers, herbicides, and seeds) in a given fieldcan lead to an over and/or under application of inputs to certain areas of the field due tothe heterogeneity of various factors within the field. The consequences of themisapplication of inputs can include unnecessary fertilizer expenses, water qualitydegradation, and depressed crop yields. An accurate assessment of the possible benefits to precision farming for a given farmfield requires the ability to determine the ‘most efficient’ application rates for inputs acrossthe field. Yield maps can help guide the determination of input management zones for afield, and subsequently, lead to the prescription of more efficient input application rates byallowing the identification of relatively high and low yielding areas of the field. Inaddition, yield maps can help quantify the affects (or lack there of) that variable rate inputapplication have had on crop yields for a given farm field. The possible benefits of having