Well it's not so much an island as a vast area with a lot of plastics of various sizes and two convergence points roughly before Japan and California with currents transporting material between them in a loop around Hawaii.

I think the islands in the bottom is New Zealand, so the small islands top left is probably Hawaii and California/Mexico barely visible at the top. That would mean that nearly a quarter of the top left rim until behind the horizon (Japan) is where the Great Pacific Garbage Patch roughly is.