Complex sentence: The island is (is also mentioned) in length and in width, with an area of within total area of the group of islands of (and are also mentioned in some references for the San Andrés), making it the largest island in the archipelago.
Split into simpler sentences: The island is (is also mentioned) in length and in width. It has an area of within the total area of the group of islands of (and are also mentioned in some references for San Andrés), making it the largest island in the archipelago.