The American shipping act requires that voyaging vessels have on board the appropriate and up-to-date chart of the area in which it is sailing. Other charts can be used for reference purposes, but only the NOAA charts (National Oceanic and Atmospheric Administration) are approved for navigation.
There are several classifications of nautical charts, done at different scales, appropriate for different types of travel. Harbor charts (1:50,000 scale or larger) are intended for navigation and anchorage in harbors and small waterways. Coastal charts (1:50,000 to 1:150,000 in scale) are for navigation inside offshore reefs and shoals, for entering larger bays and harbors, and for certain inland waterways. General nautical charts (1:150,000 to 1:600,000 in scale) are for use when the course is well offshore and positions are being determined by landmarks, lights, buoys, and characteristic surroundings. Sailing charts (smaller scale than 1:600,000, ie less detailed) are plotting charts for offshore sailing and approaching the coast from the open ocean.
Not sure which chart you need or want? Use this index to zoom in and help decide, NOAA Pacific Coast On-Line Viewer...then order from below!