1. A mapping-data analyzing method for analyzing mapping data obtained by measuring, with a spectrometer apparatus, spectra at a plurality of points on a specimen surface, comprising: a principal-component calculating step of defining at least part of spectral data obtained at each point on the specimen surface as an individual sample and performing principal component analysis, in which values at a plurality of wave numbers of each spectral data set serve as variables, to calculate the scores of a plurality of principal components for each individual sample; and a grouped-map display step of dividing the points on the specimen surface into a plurality of groups based on the scores of a plurality of principal components calculated in the principal-component calculating step, and displaying on a display device a two-dimensional or three-dimensional map indicating to which group each point on the specimen surface belongs.