ABSTRACTS 



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GEODESY. — Grid system for progressive maps in the United States. 

 William Bowie and Oscar S. Adams. U. S. Coast and Geodetic 

 Survey, Special Publ. 59. Pp. 227, figs. 6. 1919. 



This publication contains tables, with the description of "their use, 

 which make it possible to construct a "grid" on any map in the United 

 States, similar to the grids used on military maps in Europe during 

 the war. The basis for the grid system in the United States is the poly- 

 conic projection. The polyconic projection lines cannot be used to advan- 

 tage in military operations where it is necessary to compute quickly 

 the distance and direction between two points, but by means of a plane 

 coordinate system, the relation between any two or more points can 

 be obtained easily by the solution of right-angled triangles. The 

 values in the tables in this publication are the plane coordinates for 

 the intersections of 5 -minute parallels and meridians. The country 

 is divided into seven zones and any coordinate can be used for each 

 of the seven zones by merely shifting the longitude by 8 °. It was imprac- 

 ticable to have a single zone for the whole country, because of its wide 

 extension in longitude. The zones in the United States extend in a 

 north and south direction and are 9° in width. Each zone overlaps 

 the contiguous zones by i °. This makes it possible to avoid a com- 

 plete break in the plane coordinates at the margins of the zones. The 

 grid lines of two zones can be used on the maps in the overlapping 

 areas and thus provide a connection between them. 



The origin for each zone is outside of the United States and is to 

 the southwest of each zone. By having the origin in this location 

 all of the coordinates within the zone are positive. The X-coordinates 

 increase to the eastward and the Y-coordinates to the northward. 



A careful study was made of the various projections in general use 



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