When you do, learn or teach 2D graphics, you need to keep calculating coordinates, to figure out where objects should go.
Here's a simple function that will draw axis and optionally a grid on a Raphael canvas, to help you make these calculations.
The most common sizes for a Raphael Javascript canvas are (220,220) or (420,220).
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You can tell what the arguments are - they also have default values.
Just copy the code and use it as you wish.