How to blank data within a circle

I have some grid data (m*n matrix) of the surface ocean, extending to the land in some areas. I have the conterminous United States map as a circle. Is there a way that I can blank everything that lies inside the map circle?

Answer 1

[Image Analyst]

Not sure what you have. If you have vertex coordinates of some region then you can use poly2mask to create a binary mask of the image that is true in the region and false outside the region. Then you can say array2D(binaryMask) = 0 to zero it out.

[Leon]

Thank you very much. I will try it out.