Minecraft wiki entry for Map, associated text: Maps consist of square pixels arranged like pixels in a 128×128 square pattern, with each pixel representing a square portion of land. Generally, the color of a map pixel matches the color of the most common opaque block in the corresponding area, as seen from the sky. 'Minority blocks' in the target area have no effect on the color of the pixel, thus small features tend to be undetectable on zoomed-out maps.