AREA BY DOUBLE MERIDIAN DISTANCE.—The meridian distance of a traverse line is equal to thelength of a line running east to west from the midpointof the traverse line to a reference meridian. Thereference meridian is the meridian that passes throughthe most westerly traverse station.In figure 7-20, the dotted lines indicate the meridiandistances of the traverse lines to which they extend fromthe reference meridians. You can see that the meridiandistance of the initial line AB equals one half of thedeparture of AB. The meridian distance of the next lineBC equals the meridian distance of AB, plus one half ofthe departure of AB, plus one half of the departure ofBC.You can also see that the meridian distance of CDequals the meridian distance of BC, plus one half of thedeparture of BC, minus one half of the departure of DC.Similarly, the meridian distance of AD equals themeridian distance of DC, minus one half of thedeparture of DC, minus one half of the departure of AD.You should now be able to understand the basis forthe following rules for determining meridian distance:1. For the initial traverse line in a closed traverse,the meridian distance equals one half of the departure.2. For each subsequent traverse line, the meridiandistance equals the meridian distance of the precedingFigure 7-19.—Form for computing coordinatesFigure 7-20.—Meridian distances.line, plus one half of the departure of the preceding line,plus one half of the departure of the line itself. However,it is the algebraic sum that results—meaning that plusdepartures are added but minus departures aresubtracted.7-15