The vast size of universe is so hard to picture in one image because its size is unbelievably enormous compared to human and Earth. Our planet Earth has the size around 12,742 km diameter. And the nearest object to us is moon which is approximately 384,400 km from us. The number is already huge in our sense. But the size of our solar system is about 287.46 billion km and the Milky Way is around 950,000,000,000,000,000 km wide, or 105,700 light-years as the number is too large to use km as unit. It will take light 105,700 years to travel across the whole Milky Way! Consider that human has been around for only 200,000 years. And the size of Milky Way is not unique. In fact, some large galaxy can have size way bigger than Milky Way. IC1101, the largest galaxy has been found, is 6 million light-years in diameter.
Amazingly, astronomers estimated that there are around two trillion galaxies in the observable universe which is 92 billion light-years wide. So the only way to picture such enormous size in an image is to use logarithmic scales. As the picture above shows, each chunk of the circle represent a field of view several orders of magnitude larger than the one before it. So the whole observable universe is now in a single image.