Using GMT on the Statistics Computer System

The Generic Mapping Tool is a program developed for the earth sciences to produce graphs, plots, and maps. It comes with a large variety of map projections, the capability to plot functions z = f(x,y) as an apparent 3-D surface, and a large data base of continental and political boundaries, rivers and lakes.

The Statistics Department has version 3.0 installed together with the low resolution data base. There is a high resolution data base which we have not installed (but can if necessary). Documentation of version 2.1 can be found in 125 Halsey Hall.

Despite being called a "cookbook", the documentation is not especially easy to follow. Fortunately there are examples for the motivated reader. I was able to start producing plots in about 4 hours. Here are some important points:

• GMT runs in c-shell.
• GMT programs are actually shell scripts. This means that a file of UNIX commands to call the GMT commands needs to be produced within a text editor. The examples in the GMT "cookbook" are all meant to be put inside of a file. Suppose your file of gmt commands is called myprogram.gmt. To execute these commands:
  • (i) first use the command: chmod 744 myprogram.gmt
  • (ii) then use the command: myprogram.gmt
• GMT has a full set of man pages which are, in many ways, more helpful than the documentation.
• GMT produces a postscript file as its output. This file should not be manually modified in any way.