The would-be navigator setting off on a passage can select from the chart catalogue the charts required to cover all aspects of navigation and safety en route without cluttering up the ship with unnecessary folios. A gradual conversion to metric charts is taking place in many parts of the world. It is now possible to purchase both fathom and metric charts, sometimes of the same area, often of the same coastline. Needless to say it is vitally important to the navigator to know which chart is being used. This information is carried in the chart title and should be checked when the chart is purchased.
Every chart carries a title with a wealth of information of use to the navigator.
Apart from the obvious description of the area covered by the chart, other factors relating to the scale, the soundings, tidal anomalies, military areas, special areas, specific dangers and any other factors which will assist in safe navigation are listed in the chart title. Latitude and Longitude Mercator charts are covered by a 'grid' pattern indicating lines of latitude and longitude which match those on the Earth's globe. The lines which run vertically up and down the chart are meridians of longitude, and those which run horizontally across it are parallels of latitude. Thus the graduations on the top and bottom of the chart will be in degrees and minutes of longitude east or west of Greenwich and marked accordingly. On either side of the chart are the graduations for the latitude scale.