Interval will be dependent on terrain and purpose of the survey or map. Contour lines that are shown are evenly divisible by the contour interval. Spot elevations or point elevations, such as at the top of the peak, are listed for important points such as peaks, depressions, streams, road crossings, etc. They cannot deadend. Contours are perpendicular to the direction of maximum slope.
Water flow is perpendicular to contours.
The slope between contour lines is assumed to be uniform. The distance between contours indicates the steepness of the slope. Smooth lines imply gradual slopes and changes. Concentric closed contours that increase in elevation represent hills. A contour forming a closed loop around lower ground is called a depression contour.