The tide in Venice is measured and predicted on the historic zero of the city. The images indicate a tide level that can affect the walkable ground of three reference areas.
For example: because Piazza San Marco, one of the lowest points in Venice, begins to flood, it takes a tide of over 80 cm. At Rialto, in front of the public transport wharves, is needed a tide of over 105 cm while in front of the railway station, a very high area of the city, 135 cm are needed.