INTERNATIONAL. AIR MAP— -LALLEMAND. 301 



area of 1 1 1 kilometers, or 67 miles, north and south and from 82 to 68 

 kilometers (61 to 41 miles) east and west. 



In tins system the distortion, which increases as the square of 

 the distance from the central meridian, would be 36 times as small 

 in the air map as in the world map, since a sheet of the air map covers 

 only 1° of longitude instead of 6°. As, however, the scale of the air 

 map is five times as large, the errors from this source are reduced to 

 one-seventh of those in the world map. 



In order to facilitate handling, each sheet should be cut in half, 

 the cutting lines running east and west, each half measuring some 28 

 by 38 centimeters (11 by 15 inches). The two half sheets should be 

 pasted on either side of a piece of cardboard, and should have the 

 name and number of the sheet shown in a conspicuous manner. 



The Aero Club of France have prepared, this year, three trial 

 sheets of this map, covering the area to be used in the next military 

 maneuvers, with a view to obtaining the remarks of the aviator 

 officers previous to publishing a final edition. 



3. AERONAUTICAL MARKS. 



As has been previously mentioned, each mark shall show the 

 approximate longitude and polar distance of the point over which 

 the aviator is flying. The sign adopted by the committee consists 

 of half a rectangle (fig. 2) reproducing, on a sufficiently large scale, 

 the frame of the half sheet of the air map in which the mark lies. 

 The sides of this frame appear as broad lines, except the side where 

 the cut is, which is shown by a fine dotted line; thus it is easy to 

 distinguish between the upper and lower halves of a sheet. In this 

 frame a large black dot will indicate the correct position, on the sheet, 

 of the mark of the ground. 



The half rectangle is correctly oriented, the small sides, parallel 

 to the meridians, being due north and south. 



Two large figures, reading toward the north, will be marked on 

 either side of this rectangle, the left one giving the number of the 

 units of degrees of the polar distance, and the right one the number 

 of the units of degrees of the longitude. 



The combination of these two figures, forming a number easy to 

 read and remember, will be sufficient to define the number of the 

 corresponding sheet of the map, and to give the rough coordinates 

 of the mark itself. In every case where confusion might exist, each 

 of the figures should be underlined. 



Owing to the absence of the digits showing the hundreds and tens 

 of degrees of longitude and polar distance, any two marks which are 

 10° or a multiple of 10° apart will have the same number. The 

 disadvantage of this would not be of great importance. For an 

 airman to confuse two such marks would mean that he would make 



