The equirectangular panoramic image (aspect ratio of 2:1), covering 360° horizontally and 180° vertically, is commonly used as the projection type of the source images for spherical panorama viewers. Coordinates in the image relate linearly to pan and tilt angles in the real world. The poles (Zenith, Nadir) are located at the top and bottom edge and are stretched to the entire width of the image. Areas near the poles get stretched horizontally.