An exposure map of a VISTA tile. The green strips at top and bottom have a single exposure. The majority of the area (blue) has two exposures, the pink has 3 exposures, the red 4 and the white 6. The doubly or more exposed area is 1.501 sq. deg. The singly exposed green strips at top and bottom of the plot are each 1.475 deg  ×  0.092 deg = 0.135 sq. deg and can be overlapped by corresponding areas from adjacent tiles for many surveys. Assigning one of the two 0.092 deg overlap (top and bottom) to each of the adjacent tiles involved in an overlap, means that each tile, when part of a filled larger area, covers (1.017 + 0.092)  ×  1.475 = 1.636 sq. deg at least twice.