The topographical map presents much detailed, especially hypsometric information about terrain. It is, however, highly selective in what it shows, and often the detailed information that is given may not be in the desired form for direct use in geographical investiations. Particular elements of terrain, e.g. slope gradient, are important in studies of land-use, soil erosion, irrigation, flood control, transportion, economic planning and other aspects of human geography. Sometimes, special methods of depicting terrain are required by geographers. The increasing demand for these special maps in varied geographical investigations has stimulated a search for more accurate, complete or effective representation of surface characteristics. In modern cartography, photographic and lithographic techniques have made valuable contributions to the search. Concerning the relationship of human activities to relief, slope is one of the most influential elements. Therefore, the methods of slope determination and representation on maps have been the subject for much research, particularly by American geographers. The calculation of gradient between consecutive contours on a topographic map is easy, but the determination of average steepness of slopes and their representation on maps for areas of complicated relief requires much experimentation and critical analysis. Slope analysis should be based on an objective or arbitrary system, applying methods such as random sampling or grid or uniform interval sampling. However, the choice of assessment of data completely depends upon one's purposes and propositions.