Representing a circle with bits

I am having trouble with this question about data representation:

You are given the task of finding a representation for a circle in a drawing application. The circle is to be displayed on the screen, and the user can edit the location and the radius of the circle, both of which are expressed in units of pixels.

a) Specify a data representation for the circle, trying to minimize the number of bits required.

Any help would be amazing :)

[Walter Roberson]

Are fractional pixels permitted for locations or radius ?

Are negative values permitted for locations? Negative is presumably not permitted for radius.

What is the largest location or radius that needs to be supported?

[tsmewis]

I don't think the problem is calling for fractional pixels and it doesn't state the largest radius. Kind of an open-ended question. Probably why it is stumping me.