The rate of change is assumed to be positive in the direction of the increase in the value of the scalar function (up the mountain). Thus, returning to our example, water always flows in the direction opposite the direction of the gradient, whereas the most difficult climb on the mountain at any point is in the direction of the gradient. Figure 2.12 shows these considerations. The gradient on the map may indicate the direction of climbing or, if this map shows atmospheric pressure, the gradient points in the direction of increased pressure. If you were to sail in the direction of the gradient in air pressure, you will always have the wind in your face.