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From: sfeam <sfeam@users.sourceforge.net>
Newsgroups: comp.graphics.apps.gnuplot
Subject: Re: Plot a geographical map with gradient color
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Date: Fri, 25 Nov 2011 14:31:41 -0800
Organization: gnuplot development team
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Gerard Sookahet wrote:

> Hello,
> 
> I plot a geographical map with state boundaries from coordinates data
> file :
> 
> plot 'map.dat' u 1:2 w l, \
>      'map.dat' u 3:4 w l, \
>      'map.dat' u 5:6 w l, \
>      'map.dat' u 7:8 w l, \
>      [....]
> 
> If values are associated to states (polygons), is there a way to color
> them with a gradient color palette ?
> A kind of choropleth map (http://en.wikipedia.org/wiki/
> Choropleth_map).

Maybe 
   set palette ...  (pick a gradient scheme you like)
   plot 'map.dat' using 1:2 w filledcurves lt palette fraction <val1>,
        '' u 3:4 w filledcurves lt palette fraction <val2>,
        ...