In a Mercator map projection, parallels and meridians are straight and perpendicular to each other (as in all cylindrical projections). The east-west stretching on the map is accompanied by a corresponding north-south stretching, making it a conformal map projection. However, because the linear scale of the Mercator map increases with latitude, the size of geographical objects gets more distorted the closer you get to the poles.
All lines of constant bearing (rhumbs or loxodromes) are represented by straight segments. The conformality and the straight rhumb lines make the projection particularly useful for navigation. Bearings can be measured using wind roses and the corresponding directions can easily be transferred from point to point on the map.