The sea chart is a transformation of the spherical surface of the terrestrial globe onto a plane surface that we can imagine as being tangent to the point of intersection between the meridian and the Equator. The transformation is performed by transferring the meridians and parallels onto a cylinder that surrounds the terrestrial globe and is then developed onto a plane surface. After the transformation, the meridians and parallels form an orthogonal grid divided into regular intervals of equal size. However, while the length of the meridians remains unchanged with respect to their length measured on the globe, the length of the parallels increases as one moves from the Equator to the poles. The advantage of this cartographic transformation is that, while altering the measurement of longitude, it preserves the orthogonal intersections between meridians and parallels as on the terrestrial globe. In consequence, any given oblique line showing a direction of the wind rose will always meet the meridians and parallels at the same angle, exactly as it does on the terrestrial globe. This is clearly an advantage for plotting navigation routes.