Design a bird's-eye view line art illustration of a sprawling city blanketed in fog. The layout should showcase a network of streets and buildings, with the outlines of skyscrapers and residential areas emerging from the mist. The fog should create a soft, ethereal quality, blurring the boundaries between different urban elements. Include details like parks and rivers, subtly integrated into the scene, to add interest and complexity. The overall effect should be one of tranquility and mystery, inviting viewers to imagine the life happening below the fog. Use a monochromatic color scheme to maintain focus on the intricate line work and the atmospheric quality of the fog, enhancing the visual impact of the urban landscape.