This is the most often used outline of the map of the island, although how all the different landmarks depicted in various episodes could be contained on such a small space is beyond the capacity of space-time as it's currently understood. The island's oft-visited volcano isn't shown and can't be seen in the island's profile in the opening credits. The endlessly-extensive jungle with its caves and mountains and quicksand and so forth could not possibly fit in this space... not to mention the ridiculous patchy biodiversity.
Here's a map that The Professor made to track a hurricane bearing down on the island:
Here's a view of the island from an orbiting space capsule in an episode I remember quite well about the castaways trying to get themselves seen by a burning arrangement of logs spelling out SOS. It's radically different from The Professor's map and shows no volcanic peak:
Here's another map of the island, which at least shows the volcano, and resembles The Professor's map. I don't remember this episode though:
The island used in the credits in Seasons 2 & 3 is "Coconut Island" or Mokuoloe. It is located in Oahu's Kaneohe Bay.