WAAS provides very precise navigation service, with both horizontal and vertical guidance over the Continental United States (CONUS) and a large portion of Alaska, Canada, and Mexico. Other countries and regions of the world also have fielded or are fielding similar systems. WAAS and each of these other systems are known as a Satellite Based Augmentation System, or SBAS. As envisioned at its inception, WAAS today provides service from enroute through approach.