id plotting units but we need to convert them into the same units as the axes on the plot. We do this by determining the range of the x and y axes in grid units (<code>xrange_old</code> and <code>yrange_old</code>), then fixing the range of the x axis as 1 to the number of strata, adjusted by the width of the nodes, and the y axis to the number of rows in the data (again, this is possible here because each flow polygon is exactly 1 unit high).</p>
<p>We define a function <code>new_range_transform()</code> i