Cross Section Plotter: Raise Error if point is out of bounds

[lsawade]

The idea of raising an error, if a point "is not inside the region" is not as simple as I thought it may be. There are a couple of ways we could play this:

• +/- buffer around the min/max coordinates
• must be in vicinity of the of the points with a radius of at least ...

Let me know what you think.

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Note: I haven't had the error when something was out of bounds so far...