## Plotting Borders

The astBorderastBorder function is provided to draw a (line) border around your graphical output. With most graphics systems, this would simply be a rectangular box around the plotting area. With a PlotPlot, however, this boundary follows the edge of each region containing valid, unclipped physical coordinates (§21.9).

This means, for example, that if you were plotting an all-sky projection, this boundary would outline the perimeter of the celestial sphere when projected on to your plotting surface. Of course, if there is no clipping and all physical coordinates are valid, then you will get the traditional rectangular box. astBorder requires only a pointer to the Plot:

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It returns a boolean (integer) value to indicate if any invalid or clipped physical coordinates were found within the plotting area. If they were, it will draw around the valid unclipped regions and return a value of one. Otherwise, it will draw a simple rectangular border and return zero.