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<H2><A NAME="SECTION001322000000000000000">
5.2.2 Lambert Conic Conformal Projection (<B>-Jl</B> <B>-JL</B>)</A>
</H2>
<A NAME="6449"></A>
<A NAME="6450"></A>
<A NAME="6451"></A>
<P>
This conic projection was designed by Lambert (1772) and has been
used extensively for mapping of regions with predominantly east-west
orientation, just like the Albers projection. Unlike the Albers
projection, Lambert's conformal projection is not equal-area.
The parallels are arcs of circles with a common origin, and
meridians are the equally spaced radii of these circles. As with
Albers projection, it is only the two standard parallels that are
distortion-free. To select this projection in <A NAME="tex2html307"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> you must
provide the same information as for the Albers projection, i.e.
<P>
<DL>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Longitude and latitude of the projection center
</DD>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Two standard parallels
</DD>
<DT><STRONG><IMG
WIDTH="12" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
SRC="img54.gif"
ALT="$\bullet$"></STRONG></DT>
<DD>Map scale in inch/degree or 1:xxxxx notation
(<B>-Jl</B>), or map width (<B>-JL</B>)
</DD>
</DL>
<P>
The Lambert conformal projection has been used for basemaps for all
the 48 contiguous States with the two fixed standard parallels
33<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N and 45<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N. We will generate a map of the continental
USA using these parameters. Note that with all the projections you
have the option of selecting a rectangular border rather than one
defined by meridians and parallels. Here, we choose the regular WESN
region, a FANCY basemap frame, and use degrees west for longitudes.
The generating commands used were
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<PRE>
#!/bin/sh
# $Id: GMT_lambert_conic.sh,v 1.1 2001/03/21 04:10:21 pwessel Exp $
#
gmtset BASEMAP_TYPE FANCY DEGREE_FORMAT 3 GRID_CROSS_SIZE 0.05i
pscoast -R-130/-70/24/52 -Jl-100/35/33/45/1:50000000 -B10g5 -Dl -N1/1p -N2/0.5p -A500 -G200 \
-W0.25p -P > GMT_lambert_conic.ps
gmtset GRID_CROSS_SIZE 0
</PRE>
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<P></P>
<DIV ALIGN="CENTER"><A NAME="fig:GMT_lambert_conic"></A><A NAME="6589"></A>
<TABLE>
<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.7:</STRONG>
Lambert conformal conic map projection</CAPTION>
<TR><TD><IMG
WIDTH="618" HEIGHT="376" BORDER="0"
SRC="img69.gif"
ALT="\begin{figure}\centering\epsfig{figure=eps/GMT_lambert_conic.eps}\end{figure}"></TD></TR>
</TABLE>
</DIV><P></P>
<P>
The choice for projection center does not affect the projection but
it indicates which meridian (here 100<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">W) will be vertical on
the map. The standard parallels were originally selected by Adams
to provide a maximum scale error between latitudes 30.5<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N and
47.5<IMG
WIDTH="11" HEIGHT="15" ALIGN="BOTTOM" BORDER="0"
SRC="img61.gif"
ALT="$^{o}$">N of 0.5-1%. Some areas, like Florida, experience scale
errors of up to 2.5%.
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<ADDRESS>
Paul Wessel
2001-04-18
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