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Resection and its related method, ''intersection'', are used in [[surveying]] as well as in general land navigation (including inshore marine navigation using shore-based landmarks). Both methods involve taking [[azimuth]]s or [[bearing (navigation)|bearings]] to two or more objects, then drawing ''lines of position'' along those recorded bearings or azimuths.
When intersecting, lines of position are used to fix the position of an unmapped feature or point by fixing its position relative to two (or more) mapped or known points, the method is known as ''intersection''.<ref>Mooers, pp. 129–132</ref> At each known point (hill, lighthouse, etc.), the navigator measures the bearing to the same unmapped target, drawing a line on the map from each known position to the target. The target is located where the lines intersect on the map. In earlier times, the ''intersection'' method was used by forest agencies and others using specialized [[Osborne Fire Finder|alidades]] to plot the (unknown) ___location of an observed forest fire from two or more mapped (known) locations, such as forest fire observer towers.<ref>Mooers, pp. 130–131</ref>
The reverse of the ''intersection'' technique is appropriately termed ''resection''. Resection simply reverses the intersection process by using ''crossed back bearings'', where the navigator's position is the unknown.<ref>Mooers, p. 132–133</ref> Two or more bearings to mapped, known points are taken; their resultant lines of position drawn from those points to where they intersect will reveal the navigator's ___location.<ref>Mooers, p. 132–133</ref>
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