[Qgis-user] rivers growing in size as they go downhill

[Luca Galuppini]

Dear all
i have this idea of rendering a river network so that each river starts as
a very thin blue line, and the line width increases little by little as the
river goes.
i wouldn't like to modify the original file (eg cutting rivers in pieces
and give a different width to each piece) but all rivers are digitized with
the right direction so i was wondering if there is an expression to teach
qgis what is the start end of a river, and assign a wider line for any
given distance, for example:
from start to 200m - line width 0.1
from 200m to 400m - line width 0.2
from 400m and over - line width 0.3
i think this is an interesting problem because i cannot find a "from - to"
command in qgis expression language, neither i know how to properly exploit
the line direction with code, which would come useful in many other ways...
any python expert out there can help?
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/qgis-user/attachments/20150714/53ba1c74/attachment.html>