possible error in lining up each successive flight line.The longer dimension of the film is always used for theGGS.Figure 4-20 shows the usable portion of a 9- 9-inch negative after the GGF and GGS have beenfactored in.NUMBER OF EXPOSURESWhen you are flying for mosaic mapping purposes,the flight strips are usually made along the longdimension of the area being photographed. Thispractice reduces the number of turns the aircraft mustmake to photograph the strips. For example, if the areato be photographed is 5 nautical miles east and west by10 nautical miles north and south, the strips should beflown north and south.To determine the number of exposures per strip, youshould divide the ground-gained forward into the lengthof the map. When the unit of measurement is in nauticalmiles, you must convert it into feet (1 nmi = 6,080 ft).Therefore, if the area to be photographed is 10 nauticalmiles, the area when converted to feet is 60,800 (10 6,080).You add four additional frames to each strip. Twoadditional photographs should be taken just beforereaching the beginning point and two just after theending point. These four photographs allow forpossible errors in reading the beginning point and theFigure 4-20.—Usable portion of a 9- 9-inch negative.ending point of the run on the ground (from the datashown on the flight chart).You must first calculate the total number of flightstrips required to cover the area. Next, divide theground-gained sideways (GGS) by the total width of thearea to determine the total number of strips. Alwaysadd one additional strip to your calculations. Todetermine the total number of photographs (frames)required for the entire mosaic mission, multiply thenumber of photographs required for each strip by thenumber of strips.If the camera can hold enough film for the entiremission, you should have no problem. However, if thecamera does not hold enough film for the entire mission,you either have to change film between strips or beprepared to make several flights.FLIGHT LINESBefore the mapping flight, you should plot the flightlines for each run and draw them on the flight chart witha color that is easily recognizable. Draw the first flightline along the border of the area to be photographed.The remainder of the flight lines should be evenlyspaced and parallel to one another.Figure 4-21 shows a nomograph that can be used todetermine the number of flight lines required to coverthe target. This nomograph is for low-altitude coverageonly.The nomograph (fig. 4-21) is used as follows:1. Place a straightedge on the width of the area tobe searched and another along the altitude to be flown.2. Note the intersection on line R_{1}.3. Place a straightedge on the point on R_{1}andanother along the field of view of the camera lens.4. Note the intersection on line R_{2}.5. Move to R_{3}, keeping the same relative positionson segments R_{1}and R_{2}.6. Place a straightedge on the point on R_{3} andanother along the side lap required.7. Read the number of flight paths (to the largestwhole number).To determine the distance between the plotted lineson the chart, you must change the ground-gainedsideways into inches and multiply it by the scale(fraction) used on the chart. For example, if the GGSis 5,400 feet, or 64,800 inches, and the scale of the chart4-22