| 摘 要： | d. On maps where the index and intermediate contour lines do not show the elevation and relief as accurately as may be needed, supplementary contours may be used. These contour lines are dashed brown lines, usually at one-haft the contour interval for the map. A note in the marginal information indicates the interval used. They are used exactly as are the solid contour lines. e. In addition to the contour lines on maps, bench marks and spot elevation are used to indicate points of known elevation.Bench marks are usually symbolized by an X and the elevation is given at that
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