The simplest form of plotting is to draw symbols (termed markers) at a set of points. This is performed by astMarkastMark, which is supplied with a set of physical coordinates at which to place the markers:
Here, NMARK specifies how many markers to plot and NCOORD specifies
how many coordinates are being supplied for each
point. The
array “in” supplies the coordinates and the integer “type”
specifies which type of marker to plot.