A flat map is a projection of Earth's surface onto a two-dimensional plane, according to NationalAtlas.gov. Because Earth's surface curves, any projection onto a flat map creates distortions. A globe is the most accurate depiction of Earth, but impractical for most uses, whereas a flat rendering is useful but not as accurate. A flat map can be printed on paper or digitally rendered on a computer screen.
Map projections easily create different views of large or small parts of Earth, and each type of projection has advantages and disadvantages, depending on its scale and its intended use. Any projection creates distortions of distance, area, shape or direction, while different projection types minimize one or more of the distortions. One projection commonly used to create flat maps is a Mercator projection, which shows straight lines of latitude and longitude, making it useful for navigation because the compass directions are true. The National Atlas of the United States uses a Lambert Azimuthal Equal Area projection because it maintains the best depiction of area and distance. The U.S. Geological Survey uses a conformal projection, such as the Mercator or the Lambert Conformal Conic, because it more accurately depicts topography through maintaining accurate angular relationships and shapes over a small area.