NATIONAL SURVEYS AND MODERN ATLASES 159 



jection, the Transverse Mercator with the central meridian 

 2° W., and the introduction of the National Grid, uniformity 

 has now been secured. The grid serves two purposes; for the 

 smaller-scale maps it provides a national system of reference, 

 by which a point can be located by an identical reference on 

 maps of all scales; secondly, on the larger-scale plans, it pro- 

 vides data by which, with certain corrections, very large-scale 

 survey, such as is done by civil engineers, mining surveyors 

 and the like, can be carried out accurately. 



The National Grid is based on the central meridian, and 

 divides the country up, in the first place, into squares with one- 

 hundred kilometre sides. For convenience in numbering, the 

 origin of the grid is placed a little to the south-west of the 

 Scilly Isles. These squares in turn are divided into 10 km. and 

 kilometre squares, which are shown on the 1 : 25,000 and One 

 Inch maps, while the Six Inch map has the kilometre squares. 

 By estimation, therefore, references to the nearest 100 metres 

 can be read from the One Inch. 



With the introduction of the National Grid, the sheets 

 of the plans and maps are now regularly arranged; for example, 

 100 sheets of the twenty-five inch plan form one sheet of the 

 1 : 25,000 map, which in turn covers one 10 km. square on the 

 One Inch map. Thus the smaller-scale map in each case forms 

 an index to the larger. The One Inch map, however, is not 

 designed on regular sheet lines. Great Britain has a long and 

 much indented coastline, and the adoption of a regular system 

 would inevitably lead to the production of sheets showing very 

 little land surface. Consequently the sheets have been 'fitted 

 to the topography'. Their size, however, has now been stan- 

 dardized, covering 45 km. from north to south, and 40 km. 

 from east to west. The eff"ect of this has been to reduce the 

 number of sheets (the Sixth edition covers England and Wales 

 in 115, in contrast to the 146 sheets of the Fifth), and, by allow- 

 ing generous overlaps, to reduce the necessity for special 

 District maps. 



With the carrying-out of the recommendations of the 

 Departmental Committee of 1938, Great Britain now has a 

 national series of maps and plans designed on a common system, 

 which is not surpassed by those of any other country. No other 



