A great deal of confusion can arise concerning the relationship between how
gnuplot scans a binary file and the dimensions seen on the plot. To lessen
the confusion, conceptually think of gnuplot always scanning the binary file
point/line/plane or fast/medium/slow. Then this keyword is used to tell
gnuplot how to map this scanning convention to the Cartesian convention shown
in plots, i.e., x/y/z. The qualifier for scan is a two or three letter code
representing where point is assigned (first letter), line is assigned (second
letter), and plane is assigned (third letter). For example, scan=yx means
the fastest, point-by-point, increment should be mapped along the Cartesian
y dimension and the middle, line-by-line, increment should be mapped along the
x dimension.
When the plotting mode is plot, the qualifier code can include the two
letters x and y. For splot, it can include the three letters x, y and z.
There is nothing restricting the inherent mapping from point/line/plane to
apply only to Cartesian coordinates. For this reason there are cylindrical
coordinate synonyms for the qualifier codes where t (theta), r and z are
analogous to the x, y and z of Cartesian coordinates.
