How can I compare two curves statistically?

Question

I have points in a 2D space, and each point has X and Y coordinate. These points are stored in an array. There are two separate arrays each array has n points with X and Y coordinate. The points in those arrays represent two curves, i.e. the first array represent the 1st curve and second array represents the 2nd curve. I want to compare those two curves statistically, or with some measure, for example, the circle is measured with radius, line with a length, etc. likewise I want to compare those curves with that kind of characteristic which can be represented by just one number.