A computer-implemented method for converting rock classification maps for modeling, the method comprising: obtaining rock classification map information acquired as physical characteristics of the rock in a region, the rock classification map information defining a rock classification map stored as a raster image, the rock classification map including non-interpolatable classification of rocks in the region, wherein different non-interpolatable classifications of rocks in the region are provided by different pixel values of the rock classification map, wherein the pixel values of the rock classification map providing the non-interpolatable classification of rocks in the region includes the different pixel values being discontinuous and interpolation of two different pixel values providing incorrect classification of rocks in the region; generating a gridded index map from the rock classification map, the gridded index map including a grid of cells that represents the region, the cells including digitized values of the non-interpolatable classification of the rocks in the region; converting the non-interpolatable classification of rocks in the region provided by the rock classification map into lithology values for modeling based on matching between the digitized values of the gridded index map and values of a rock-lithology library, the rock-lithology library establishing correspondence between different digitized values of the non-interpolatable classification of the rocks in the region and different lithology values, wherein the rock-lithology library establishes correspondence between a first digitized value of the non-interpolatable classification of the rocks in the region and a first lithology value, and the non-interpolatable classification of the rocks in the region for a first cell of the gridded index map including the first digitized value is converted into the first lithology value based on the correspondence between the first digitized value and the first lithology value established by the rock-lithology library; and generating a lithologic representation of the region based on the lithology values of the gridded index map. obtaining rock classification map information acquired as physical characteristics of the rock in a region, the rock classification map information defining a rock classification map stored as a raster image, the rock classification map including non-interpolatable classification of rocks in the region, wherein different non-interpolatable classifications of rocks in the region are provided by different pixel values of the rock classification map, wherein the pixel values of the rock classification map providing the non-interpolatable classification of rocks in the region includes the different pixel values being discontinuous and interpolation of two different pixel values providing incorrect classification of rocks in the region; generating a gridded index map from the rock classification map, the gridded index map including a grid of cells that represents the region, the cells including digitized values of the non-interpolatable classification of the rocks in the region; converting the non-interpolatable classification of rocks in the region provided by the rock classification map into lithology values for modeling based on matching between the digitized values of the gridded index map and values of a rock-lithology library, the rock-lithology library establishing correspondence between different digitized values of the non-interpolatable classification of the rocks in the region and different lithology values, wherein the rock-lithology library establishes correspondence between a first digitized value of the non-interpolatable classification of the rocks in the region and a first lithology value, and the non-interpolatable classification of the rocks in the region for a first cell of the gridded index map including the first digitized value is converted into the first lithology value based on the correspondence between the first digitized value and the first lithology value established by the rock-lithology library; and generating a lithologic representation of the region based on the lithology values of the gridded index map.