The correct answer is - isobar.
On this map, the lines represent isobars. The isobars are lines that closed and circular, connecting the dots of places that have the same air pressure. On this map, as we can see, is represented the air pressure in the United States.
From what can be seen on this map, the air pressure in the western part of the country is high air pressure, throughout all of that half of the country. The eastern half is more mixed, with the isobar marked with 1016 being the areas with high pressure, while all the others are low air pressure zones.