Flat maps of the United States are not perfectly accurate because the Earth is spherical. Even maps of small sections of the globe are slightly inaccurate because a flat representation cannot capture the natural curves of the land.
Cartographers use a variety of techniques to make flat maps as accurate as possible. A cartographer considers the shape of a location, distance between locations, area and direction a landmass is facing when creating a map. Since not all of these factors can be represented with complete accuracy on the same flat map, the cartographer considers the specific type and purpose of the map to determine what aspects are most important.