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<H2><A NAME="SECTION00373000000000000000">
1.7.3 Mercator projection</A>
</H2>
<A NAME="1706"></A>
<A NAME="582"></A>
<P>
Despite the problems of extreme horizontal exaggeration with
latitude, the conformal Mercator projection (<B>-JM</B>) remains
the stalwart of location maps used by scientists. It is one
of several cylindrical projections offered by <A NAME="tex2html132"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A>; here we
will only have time to focus on one such projection. The
complete syntax is simply
<BR>
<P>
<B>-JM</B><I>width</I>
<BR>
<P>
To make coastline maps we use <A NAME="tex2html133"
HREF="../pscoast.html"><I><B>pscoast</B></I></A><A NAME="2377"></A> which automatically will
access the <A NAME="tex2html134"
HREF="http://www.soest.hawaii.edu/gmt"><B>GMT</B></A> coastline data base derived from the GSHHS
database<A NAME="tex2html130"
HREF="footnode.html#foot1707"><SUP>1.4</SUP></A>. In addition
to the common switches we may need to use some of several <A NAME="tex2html135"
HREF="../pscoast.html"><I><B>pscoast</B></I></A><A NAME="2389"></A>
-specific options (see Table <A HREF="node41.html#tbl:pscoast">1.2</A>).
<P>
<BR><P></P>
<DIV ALIGN="CENTER"><A NAME="613"></A>
<TABLE>
<CAPTION><STRONG>Table 1.2:</STRONG>
Main options when making coastline plots or overlays.</CAPTION>
<TR><TD>
<DIV ALIGN="CENTER"><TABLE CELLPADDING=3 BORDER="1">
<TR><TD ALIGN="CENTER" COLSPAN=1><FONT SIZE="-1">
<I>Option</I></FONT></TD>
<TD ALIGN="CENTER" COLSPAN=1><FONT SIZE="-1"> <I>Purpose</I></FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-A</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Exclude small features or those of high hierarchical levels </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-D</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Select data resolution (</FONT><FONT SIZE="-1"><B>f</B>ull, </FONT><FONT SIZE="-1"><B>h</B>igh, </FONT><FONT SIZE="-1"><B>i</B>ntermediate, </FONT><FONT SIZE="-1"><B>l</B>ow, or </FONT><FONT SIZE="-1"><B>c</B>rude) </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-G</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Set color of dry areas (default does not paint) </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-I</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Draw rivers (chose features from one or more hierarchical categories) </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-L</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Plot map scale (length scale can be km, miles, or nautical miles) </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-N</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Draw political borders (including US state borders) </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-S</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Set color for wet areas (default does not paint) </FONT></TD>
</TR>
<TR><TD ALIGN="LEFT"><FONT SIZE="-1">
</FONT><FONT SIZE="-1"><B>-W</B> </FONT></TD>
<TD ALIGN="LEFT"><FONT SIZE="-1"> Draw coastlines and set pen thickness </FONT></TD>
</TR>
</TABLE><FONT SIZE="-1">
<A NAME="tbl:pscoast"></A></FONT></DIV></TD></TR>
</TABLE>
</DIV><P></P>
<BR>
<P>
One of <B>-W</B>, <B>-G</B>, <B>-S</B> must be selected. Our first coastline
example is from Latin America:
<P>
<PRE>
pscoast -R-90/-70/0/20 -JM6i -P -B5g5 -G180/120/60 >! map.ps
</PRE>
<P>
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<ADDRESS>
Paul Wessel
2001-04-18
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