There are two digitizing techniques which are operable without human interpretation of contour-mapped data and which thus may be performed semi-automatically; line following and raster scanning. After a comparison of these techniques the author concentrates on raster scanning, as this technique facilitates creation of matrix data, the data structure most widely used in spatial analysis performed by digital computers. The author proposes the quantization method of computing matrix data and shows that quantized data may be used not only for overall computations but also to determine geometrical properties of surfaces - giving the possibility of error estimation-shown by the contour map. In particular such an approach enables pre-determination of a scanning parameter track spacing before digitizing to satisfy the required accuracy of analysis. The different aspects of utilising data obtained by raster scanning are discussed; storage, display in contour map form - the algorithm to produce the type of map where the contour lines pass exactly through the sample points taken during scanning is included
