INTERNATIONAL. AIR MAP— LALLEMAND. 299 



appreciable advantage. In many countries maps on this scale 

 already exist, but having been produced with special objects, either 

 economical or strategical, they only imperfectly satisfy the wants 

 of airmen. A new special map is therefore necessary. A provisional 

 model, submitted by the Aero Club of France, showing specially the 

 typical buildings by their profile in black, was adopted by the com- 

 mittee. 



At my suggestion it was decided that the new map should be a 

 subdivision of the International Map of the World, on a scale of 1 

 to 1,000,000/ for the production of which, on the happy initiative 

 of England, a common agreement was recently arrived at between 

 the principal States of the civilized world. 



The " world map" would furnish index diagrams for the fitting 

 together of the sheets of the "air map," It would also be useful 

 for drawing up schemes for long journeys, or for measuring the dis- 

 tance between two widely separated points and obtaining the orienta- 

 tion of the line adjoining them. 



The "world map" is to be designed with the meter as unit of 

 lengths, and the meridian of Greenwich as origin of the longitudes. 

 The sheets are limited by meridians drawn out at successive intervals 

 of 6°, extending from Greenwich, and by parallels traced out at suc- 

 cessive intervals of 4°, reckoning from the Equator. 



The meridian sectors, from longitude 180° east or west of Greenwich, 

 are given numbers from 1 to 60, increasing in an easterly direction. 

 The zones, extending from the Equator on each side to 88° latitude, 

 are given letters from A to V preceded by the words "north or south." 

 The polar areas are lettered Z. Each sheet shall bear the name of 

 the locality or most important geographical feature on the territory 

 represented, and in addition the number of the sector and the letter 

 of the zone crossing each other on the sheet in question. For example, 

 the sheet of Paris will be named "North M. 31." 



For each sheet the corresponding part of the terrestrial ellipsoid 

 is represented by a modified polyconic projection constructed on its 

 central meridian. The meridians are straight lines and the parallels 

 arcs of circles the centers of which lie on the prolongation of the cen- 

 tral meridian, so that the radius of each one is equal to the generatrix 

 of the cone tangent to the ellipsoid along the corresponding parallel. 

 The alterations of angles, distances, and areas are practically small 

 enough to be neglected. 



On the other hand, the sheets of the air map will be limited by 

 meridians and parallels at successive intervals of 1°, reckoned from 

 the same origins as for the world map. Each sheet should cover an 

 area of 1° of longitude and 1° of latitude. Twenty-four sheets of this 

 map will therefore cover the same area as the corresponding sheet of 



1 That is not to say that the air map will be an exact amplification of the world map, but nearly so. 



