While creating a sketch, what you identify positive and negative space?
you identify positive and negative space.

Explanation:

Positive space -- the space in drawing or sketching where the main focus on the picture is located. Positive cannot function without negative, as together, along with an artist's creative and intelligent part, they form a very complex picture with numerous details that make the piece of art as vivid as possible and it seems like it tells a story.

Negative space -- in art, negative space is the space that belongs to the background. It functions very well with positive space if it's used creatively by the artist. Negative space is never empty, and it's role is to circle the picture and makes it whole. If an artist would draw only the main thing, without negative space, it would look boring and empty.