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RE: st: Graphing some Isobars..

From   "Nick Cox" <>
To   <>
Subject   RE: st: Graphing some Isobars..
Date   Thu, 23 Sep 2004 14:53:30 +0100

I agree with Stas. At present, you 
need to go outside Stata for this. 

As a geographer and word-nut, I can 
comment on the terminology here. 
None of what follows helps solve the 
problem, or indeed any other problem, 
so you can bail out here. 

Isobars are strictly lines of equal (atmospheric) 
pressure on a map. Contours were originally 
lines of equal (surface) altitude, but 
clearly are understood much more broadly. 
Some geographers have used "isarithm" 
or "isopleth" as general terms; the 
latter is perhaps more widespread, and 
can be contrasted with "choropleth" 
for maps in which values are shaded by 
areas (e.g. states or counties). 
Tukey hit the nail on the head in calling 
the last "patch maps". A disadvantage 
of "choropleth" is that many people's memories 
of studying photosynthesis when young makes
them write "chloropleth". 

In days when some scholars used to show 
off what Greek they know, or had found 
in a dictionary, almost every kind of 
line showing constant values was given 
a distinct name: some have flourished 
in limited fields, e.g. isotherm (temperature), 
isohyet (rainfall), isobath (depth). 
Some failed to get off the ground, e.g. 
isonoet (lines of equal IQ), found I believe 
only in one study of IQ patterns in Tasmania. 


Stas Kolenikov
> Another name I know this under is the countour plot. There are some
> routines that go back into prehistoric period of Stata graphics (i.e.,
> before 8), but they are way too basic. This is a long awaited feature
> for me, and so far S-Plus/R is much better in graphs of this kind.


> > I have three variables, X Y & Z (all 3 continuous)... How 
> can I graph
> > 'isobars', ie linkings (x,y) so that Z(x,y) is constant

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