Hachures

Perhaps the first serious, scientific depiction of terran was the use of hachures.  While these could have a bad reputation, "which, as ordinarily used, are only a sort of conventional symbol, intended to indicate vaguely the existence of a hill or ridge , or series of ridges , and too frequently having a perverse resemblance to a cluster of caterpillars crawling over the surface" (complaint about Wheeler Survey topography in the US West during the 1870's).  As perfected by the Swiss, hachures can produce beautiful maps.

 

The Swiss cartographer Eduard Imhof produced a classic book on relief depiction, and set 5 rules for hachures:

  1. follow the direction of steepest gradient
  2. arranged in horizontal rows
  3. length corresponds to the local horizontal distance between assumed contours of a certain interval
  4. width is thicker for steeper slopes
  5. density remains constant throughout the map area (dropped for oblique illumination).

For small-scale map (less than 1:500 000 according to Imhof), the rules may be relaxed in get a more suggestive representation.

 

1907 Swiss map of Bern, with topography indicated with hachures (from Wikipedia)
1883 Wheeler Survey map of Yosemite (courtesy David Rumsy Map Collection)
1877 Swiss map, with three colors of contours (from Wikipedia)

 

A number of people, for various reasons, have attempted to create artistic hachures via algoritms in the GIS (see the references at the bottom of this page).   

The basic principle for deriving the hachues would be relatively simple, by computing slope and aspect.  This map shows flow directions computed with MICRODEM.

To get hachures, the program would just have to:

  • Vary thickness/length of the lines depending on slope
  • Adjust or eliminate the arrowheads
  • Remove symbols in "flat" terrain
  • Randomize slightly the position of the vectors

Whether the end results would be worth the time expended remains an open question.  This does clearly demonstrate the relationship between contours lines and flow directions, and terrain shadowing.  For a GIS context, the terrain is usually just the backdrop for data display, and the hillshade/reflectance map already does a very good job of that.

 

 


References


Last revision 11/26/2017