Photos from Magellan show an area of Venus about 1,145 miles wide by 1,002 miles long. In a landscape dominated by volcanism, the most prominent geologic structures are called arachnoids, which range from 37 to 155 miles in length. Arachnoids are marked by concentric ridges and fractures. They frequently are found in groupings that form networks connected by fractures. The black lines are areas Magellan did not map.