The surface of Venus has many features similar to those on Earth. Most of the planet is dominated by relatively low-lying plains characterized by abundant volcanic structures, but there are also continent-size highland regions with mountain ranges, volcanoes, and rift systems. The largest highland region, named Aphrodite Terra, straddles the equatorial region of Venus. It is about the size of Africa. The highest point on the planet, lying in the Maxwell mountains, rises about 11 km (7 mi) above the average surface elevation. It might be noted that the Maxwell range is named after physicist James Clerk Maxwell. It is the only Venus feature named after a man. All other features on the planet are named after women, following planetary nomenclature rules established by the International Astronomical Union. The density of impact craters on Venus is similar to their density on Earth, indicating a surface age of about 800 million years and suggesting that the surface may still be undergoing active geological processes such as quakes and erupting volcanoes. Many of the impact craters have long outflows extending from the rim, probably representing large volumes of very fluid material produced during the extremely energetic event. Because the dense atmosphere screens out smaller meteors and other impactors, the smallest impact crater on Venus is about 3 km (1.9 mi) wide. Mountain ranges, long faults, and deep troughs on the planet indicate that horizontal surface movement has occurred there. Among the most complex types of terrain identified on Venus are raised regions of the surface that are characterized by complexly intersecting sets of faults and ridges. These regions, called tesserae from the Latin word for "tile," may result from long episodes of compression and extension of the surface. Larger circular features on the surface, more than 300 km (185 mi) across, are surrounded by concentric ridges and troughs. These features, called coronae from the Latin word for "crown," are hot spots formed over hot material rising from deep in the planet's interior, in a way similar to the formation of the Hawaiian islands on Earth.