113 HYDROGRAPHIC MANUAL PaGE 6 



able area. In the legend of Coast and Geodetic Survey charts under the heading 

 "Authorities" will be found information of value relative to the dates of surveys. It 

 should be noted that limits of surveys do not necessarily correspond with chart limits, 

 and on small-scale charts, especially, the results of many surveys of various areas and 

 dates may be embodied. 



In addition to the dates given in the authorities note, there are three important 

 publication dates on every chart issued, whose significance should be understood. 

 These are termed edition date, print date, and hand-correction date. 



The edition date appears in the publication note in the center of the lower margin 

 of the chart. It is changed when a new edition is issued. A new edition is issued 

 whenever corrections to the chart are of such extent and importance as to make all 

 previous copies of the chart obsolete. The date does not necessarily indicate that the 

 chart has been reconstructed, nor does it necessarily have any reference to the dates of 

 the surveys. 



The print date is the date, or the farthest to the right of a series of dates, appearing 

 in the lower left-hand margin of the chart. The printing plates are corrected for all 

 essential applicable information received prior to this date. 



The hand-correction date, or date of issue, is impressed by rubber stamp in the lower 

 right-hand margin of the chart near the printed note which reads "Lights, beacons, 

 buoys, and dangers corrected for information received to date of issue." All changes 

 in aids to navigation, newly discovered dangers, and other important data which are 

 published in the Notices to Mariners subsequent to the print date are added by hand 

 before issue. 



113. The Hydrographic Survey 



The principal object of all hydrographic surveying is to secure information con- 

 cerning the water areas and the adjacent coasts for the compilation of nautical charts 

 and Coast Pilots and for their correction. 



1131. Combined Operations 



Hydrography is that branch of applied science which deals with the measurement 

 and description of the physical features of the navigable portion of the earth's surface 

 and adjoining coastal areas, with special reference to their use for the purpose of 

 navigation. As such, it embraces a great variety of activities including: Astronomic 

 observations, triangulation, and topographic surveys of the coasts; the observation and 

 study of tides and currents; magnetic surveys; oceanography; the measurement of the 

 depths of navigable waters; and the collection of various kinds of data needed in 

 compiling and correcting nautical charts and Coast Pilots. 



In a broad view, all of the above activities are included in hydrographic surveying, 

 and a hydrographer will eventually be called on to perform each of them. In the 

 Coast and Geodetic Survey many of these operations at times are conducted by sepa- 

 rate parties, each organized and instructed especially for one specific duty, and because 

 of this not all of the operations are considered as being included in hydrographic 

 surveying. 



In the Coast and Geodetic Survey the combined activities of a hydrographic party 

 are termed combined operations, and a sm^vey party whose principal work is sounding 

 is said to be engaged on combined operations when its duties include other activities 

 such as triangulation, topographic surveying, tide and current observations, and 

 magnetic observations. 



