Everything is fine except: 1. You should change "showing" to "shows." Use the Simple Present to describe enduring qualities, and conjugate it as "shows" to match the singular "each." 2. We normally collocate "compose" with "of" rather than "by." 3. Add "different" before "country" to clarify that the panels don't all show the same country. The figure is composed of several panels, each of which shows a different country.

Hi Angela, you can say: The figure is composed by several panels, each of which shows a country. Hope this helps! :)

For my part, the use of “each of which” are correct in both sentences.

composed 'of' several panels each of which 'show' ... I think