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I am preparing a map which is concerned with showing two line features and there relative location to each other. The line features are 20 m apart and at a scale of 1:50 000 or bigger on A3 I want to show which the lines a little separated from each other. The features follow a common path, but change sides irregularly, i.e. one feature is on the south for while, then the north, then th common path changes north south and the line features then alternate between sitting on the east or west of the path.

I would like to do this in QGIS. Is there some sort of automagical dynamic offset control for lines? I can imagine how to rotate symbols based on an adjacent feature, but this is a bit more complicated. I can imagine a method of breaking one line up into segments and then creating an index of those segments compared to the other line acting as an anchor. The index might then be used to specify the offset, however this is a sort one time run solution. Rather just looking for the elegant cartographic solutions, if they exist.

ta

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up vote 3 down vote accepted

If the point is just to show it in map layout - what about line buffers? If you create lets say 200m buffers for both lines and then erase both from each other you will get approx 20m thick "lines" (polygons) 200m far from each other.

Btw in QGIS:

  1. select one line
  2. Vector - Geoprocessing Tools - Buffer(s)
  3. select second line, repeat step 2
  4. Vector - Geoprocessing Tools - Difference buffer1 - buffer2
  5. repeat step 4 - buffer2 - buffer1

Done.

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