1. An area analysis method, comprising the steps of: dividing an area to be analyzed into a plurality of small regions and measuring the small regions photometrically to obtain spectrums of the respective small regions; extracting a plurality of principal components from said obtained spectrums of the respective small regions; computing principal component marks of each of said extracted principal components for each of the small regions; classifying the plurality of small regions into a plurality of small region groups so that the small regions whose principal component marks of specified principal components exceed a predetermined value are included in identical ones of the small region groups; and determining the substances constituting the classified small region groups based on the principal component marks.