What do areas enclosed by a long and short dashed magenta lines indicate?

At 0726 you depart Lake Montauk with light 1 close aboard and set course 065° pe...

At 0817 your GPS indicates a position of LAT 37°01.6'N, LONG 75°31.7'W. You are...

At 0829 your position is LAT 41°02.9'N, LONG 72°57.4'W. You are making turns for...

At 0919 you are in Chesapeake Channel between Trestle B and Trestle C of the Che...

At 0919 your position is LAT 37°00.0'N, LONG 75°30.0'W. You are on course 270°T...

(5.8.2.1A8-4) At 0943, your position is LAT 41°14.8'N, LONG 71°54.3'W. You are t...

At 1014 you depart the entrance to Lake Montauk with light "1" close aboard. You...

At 1014 you depart the entrance to Lake Montauk with light "1" close aboard. You...

At 1113 you are in the entrance to Great Salt Pond on Block Island with buoy "5"...

At 1256 your GPS position is LAT 36°57.0'N, LONG 75°41.0'W. At 1336 your positio...