Most modern navigation relies primarily on positions determined electronically by receivers collecting information from satellites. Most other modern techniques rely on crossing lines of position or LOP.A line of position can refer to two different things: a line on a chart and a line between the observer and an object in real life. A bearing is a measure of the direction to an object.If the navigator measures the direction in real life, the angle can then be drawn on a nautical chart and the navigator will be on that line on the chart.In addition to bearings, navigators also often measure distances to objects.On the chart, a distance produces a circle or arc of position. Circles, arcs, and hyperbolae of positions are often referred to as lines of position.
If the navigator draws two lines of position, and they intersect he must be at that position.A fix is the intersection of two or more LOPs.
If only one line of position is available, this may be evaluated against the dead reckoning position to establish an estimated position.
Lines (or circles) of position can be derived from a variety of sources:
celestial observation (a short segment of the circle of equal altitude, but generally represented as a line),
terrestrial range (natural or man made) when two charted points are observed to be in line with each other,
compass bearing to a charted object,
radar range to a charted object,
on certain coastlines, a depth sounding from echo sounder or hand lead line.
There are some methods seldom used today such as "dipping a light" to calculate the geographic range from observer to lighthouse
Methods of navigation have changed through history.Each new method has enhanced the mariner’s ability to complete his voyage.One of the most important judgments the navigator must make is the best method to use. Some types of navigation are depicted in the table.