What do the lines making a circle around the low-pressure area indicate?

map of the united states containing an area noted with a capital h with two lines of various contours making loops around the h. another area is noted with a capital l with three lines of various contours making loops around the l. below the l are two curved lines that form an acute angle. one line has blue triangles on it and the other line has red semicircles on it. the triangles and semicircles are both on the right side of the lines and they are facing east. there is a gray area surrounding the outside of the acute triangle. there is more gray next to the line with the red semicircles.

an occluded front

areas of equal altitude

areas of equal pressure

a stationary front