The Cook Islands.
20 N 80 W is near Cuba.
Delaware is a state of the US found in the Atlantic Coast. The state latitude is 39.0000° N and a longitude of 75.5000° W.
Chad
Lines of latitude allow any position north or south of the Equator to be found with reasonably accuracy. Which, along with lines of longitude, are extremely important in the navigation of shipping.
20 N 80 W is in the Caribbean Sea, between the Cayman Islands and Cuba. As the question states an (single) island! I must assume that it is the single island of Cuba.
That point is in west-central Jolo Island in the Philippines.
20 N 80 W is near Cuba.
Latitude: 50°38'00" Longitude: 126°41'00" Relative Location: N. of Swanson Island, W. of Crease Island, Range 1, Coast Land District
There is no island located at these coordinates. The Free and Sovereign State of Sonora in Mexico is found here.
13 S 16 E is Huambo, Angola, Africa (not an island country).
Every point on the surface of the earth has latitude and longitude. If the latitude and longitude of a point are given and they're sufficiently accurate, the point can be found within less than an inch, anywhere on earth.
Delaware is a state of the US found in the Atlantic Coast. The state latitude is 39.0000° N and a longitude of 75.5000° W.
You have found the absolute location.
Chad
Tucson, AZ may be found here on a map: Latitude: N 32° 13' 18.2744" | Longitude: W 110° 55' 35.3244"
Longitude are the vertical lines found in a map or globe while latitude are the horizontal lines.
If you use longitude and latitude you can find a location easily on the globe.