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.