2. PLANS AND PREPARATIONS 

 Table 5. — Scale equivalents for laying- out survey sheets 



(Change 1) 27 



1 Nautical mile 

 1 Statute mile = 



r 6,076.10 ft. or 1852.0 m. 

 5,280 ft., or 1609.3 m. 



tiplying the dimensions of the sheet by the 

 number of miles at the selected scale. For 

 example, a sheet 36 by 54 inches on a scale 

 of 1 :20,000 will include an area 9.8 by 14.8 

 nautical miles. 



If planetable topographic or graphic con- 

 trol surveys are required, the location of the 

 sheets should be shown in the sheet layout. 



2-21 Sheet orientation. — All hydro- 

 graphic sheets shall be laid out so that the 

 projection lines are approximately parallel 

 with the sides of the sheet, except when such 

 a layout is extremely uneconomic or imprac- 

 ticable. The reason for this is that a cloth- 

 mounted sheet distorts almost uniformly 

 along its axes and if the sheet is laid out 

 with the projection lines parallel to the 

 edges, distortion is comparatively easy to 

 compensate for in chart compilation. With 

 a skewed projection it is much more trouble- 

 .some and, in addition, such a sheet is in- 

 convenient to handle. North shall always be 

 considered the top of the sheet, whether or 

 not the projection lines are parallel to the 

 edges of the sheet. 



2-22 Sheet .sizes. — The standard size for 

 all hydrographic sheets shall be 36 by 54 



inches and they shall ordinarily not exceed 

 this size (see 1-8 and 6-3). Chiefs of Party 

 are authorized to increase the sheet size to 

 36 by 60 inches in exceptional cases, but ap- 

 proval must be obtained from the Director 

 before using a sheet larger than 36 by 60 

 inches. Flat sheets 36 by 60 or 42 by 60 

 inches will be furnished on requisition to the 

 Washington Office and shall be used for boat 

 sheets and smooth sheets. Use of other types 

 of paper for this purpose is not authorized. 

 The 42-inch width may be used when con- 

 siderations of control make it advisable ; 

 however, hydrography should be limited to 

 an area 30 inches wide in order that the 

 sheet may be trimmed after verification and 

 review. 



Calibi-ntioii .sheets should be constructed on 

 alumiiuun-mounted i)aper or on mylar. The 

 ahiminuni-mounted paper best satisfies the dis- 

 tortion problem but sheet size is restricted to 

 24 by 31 inches. The paper must be mounted 

 on both sides of the aluniiiunn ; a single inount- 

 ino; will warp the sheet. Grained mylar is 

 available in sizes up to 3(> by 60 inches. 



Unless otherwise instructed, all planetable 

 topographic or graphic control surveys ahall 



