Because the Earth rotates, the actual shape is slightly oblate. The radius at the Equator about 10 km higher than average, and the radius at the poles about 20 km lower than average. Great circles are the intersection of Earth's surface with planes that pass through the center of the Earth. They are measured in degrees W or E Long. The shape of the orbit is nearly circular, but not quite.
Earth is slightly closer to the Sun during the Northern Hemisphere winter.
Surprisingly, the greatest annual variation is in the temperate, mid-latitude zones. In Polar Regions, the intensity of solar radiation throughout the year is always low, and there is not that much variation from season to season. There are a variety of ways to make maps, but all of them involve some distortion of shape, distance, or direction. Maps of Earth are constructed by projecting light rays from either the rotational center or the center onto screens of various shapes refer to Fig. You can visualize this type of map as peeling and splitting the Earth like an orange, then flattening it out.