What information can be determined by observing the spacing of contour lines?

The information that can be determined by observing the spacing of contour lines on a topographic map is relative steepness.  It's relative steepness because without knowing the map's relief or the map's contour interval, all that a user can do is see that certain areas are steeper than others.  Contour lines that are closely spaced indicate a steeper section than contour lines that are widely spaced.  In order to know exactly how steep a particular slope is, the map user will need to know the contour interval.  The contour interval is the change in elevation from one contour line to the next contour line.  Once the elevation change is known, the user would need to know what the map's scale is. By knowing the contour interval and the map's scale, a person can then calculate the actual steepness of a slope. 
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