In general, a plot has an x-axis increasing from left to right and a y-axis increasing from bottom to top. If the paper is turned so that the long dimension of the paper is parallel to the x-axis then the plot is said to have Landscape orientation. If the long dimension of the paper parallels the y-axis the orientation is called Portrait. (Think of taking pictures with a camera and these words make sense). All the programs in GMT have the same default orientation, which is Landscape. Use -P to change to Portrait (Note that PAPER_MEDIA is a user-definable parameter, by default set to Letter (or A4). For other paper dimensions you must change this value accordingly).