1. A method of identifying mapping of a paper machine actuator in a paper making process, the method comprising a) performing a mapping test to obtain a mapping test result, b) forming a non-linear shrinkage profile of the paper web, c) eliminating the effect of the non-linear shrinkage profile from the mapping test result, d) forming a straight line from the result obtained in step c), e) forming a first mapping model which does not include the effect of the non-linear shrinkage profile f) comparing the straight line formed in step d) with the mapping model formed in step e) to produce a first linear mapping error, g) forming a second mapping model utilizing the non-linear shrinkage profile, h) comparing the mapping model formed in step g) with the result of the mapping test to produce a second linear mapping error, i) forming the total error of linear errors from the difference between the first linear mapping error and the second linear mapping error, j) determining the magnitude allowed for the total error of linear errors, and k) comparing the magnitude of the total error of linear errors produced with the allowed magnitude of the total error of linear errors, and if the total error of linear errors is sufficiently small, concluding that the linear errors indicate a linear error in the mapping model, and that the currently used non-linear shrinkage profile indicates the non-linear shrinkage profile to be used in the mapping model with sufficient accuracy, in which case the linear error and non-linear shrinkage profile thus determined are used in the mapping model, and if the total error of linear errors is too great, forming a new non-linear shrinkage profile and repeating method steps c) to k).