1. A method of classifying and retrieving measurement data derived from a plurality of rock core and/or plug samples comprising: a. scanning sections prepared from each sample at predetermined intervals to provide a plurality of images; b. calculating the spatial variability of measurements of at least the main characteristics of the images prepared from each of the samples to provide at least one variographic parameter for each of the characteristics for each of the samples; c. entering information into a database that includes a unique sample identifier for each of the plurality of samples and the at least one variographic parameter calculated in step (b) in association with the sample identifier; d. sorting and retrieving data corresponding to the main image characteristics based on at least one of the variographic parameters.