236 HYDROGRAPHIC MANUAL PaGE 94 



236. Connection With Control of Other Agencies 



Permanently marked triangulation and traverse stations established by the 

 United States Corps of Engineers, other agencies, or local engineers, encountered during 

 the normal progress of a topographic survey that have not been connected to the federal 

 network of control established by this Bureau, shall be located by the topographic 

 survey so that their positions are available on the established geodetic datum. Such 

 stations should be located with particular accuracy — ^locations as follows will be con- 

 sidered satisfactory: 



(o) By graphic triangulation with a perfect intersection of at least three cuts. 



(6) By a closed traverse which requires no adjustment — provided that adjusted traverses com- 

 plying with the requirements may be tolerated in areas where a 5-mile spacing of the triangulation 

 control is permitted (see 2231). 



Permanently marked bench marks, and control stations of other agencies known 

 to have been connected by triangulation to the federal network, but for which the 

 topographer does not have the positions, which are encountered during the topographic 

 survey shall also be located. Bench marks of the first- and second-order level net and 

 tidal bench marks established by this Bureau, as well as bench marks established by 

 the Corps of Engineers, other agencies, and local engineers should be included. No 

 special effort need be made to locate these with an accuracy greater than* that ordinarily 

 obtained in the topographic survey. 



The triangulation and traverse stations and the bench marks which are located 

 by topography shall be described on Form 524, in accordance with 2351. 



2361. Uncontrolled Maps and Blueprints 



Existing maps or blueprints of surveys of special areas may be submitted to 

 supplement topographic surveys or as indicative of changes which have taken place 

 in the areas. In either case a field inspection shall be made on the ground to determine 

 and note which features shown on the plan represent actual conditions; planned im- 

 provements or construction, if nonexistent at the time of the inspection, shall be 

 plainly indicated on the copy transmitted. Explanatory notes shall be made wher- 

 ever necessary for a complete understanding of the conditions at the time of the 

 inspection. The date of the examination shall be noted. No map or blueprint should 

 be submitted in lieu of making a topographic survey unless it complies approxi- 

 mately with the requirements for topographic surveys of this Bureau, taking into 

 consideration the larger scale of the plan. The topographer or Chief of Party shall 

 state over his signature that an examination has been made on the ground, and that 

 the plan, as corrected or amended, represents actual existing conditions at the time. 



If the map or sketch is submitted to supplement a topographic survey it should 

 be submitted at the same time and be considered a part of the records accompanying 

 the topographic survey. 



Complete details shall be given as to the source of the map or blueprint and if 

 this has an identifying number it should be included; the date of the survey and the 

 scale shall be furnished if known. 



Maps and blueprints of surveys of local areas are frequently uncontrolled geo- 

 graphically or are based on a local control which is not connected with the federal 

 network of triangulation. Such a map or blueprint is useless unless a sufl&cient num- 

 ber of points shown on the map or blueprint are located by triangulation or topography 

 to permit its correlation with the surveys of this Bureau. Three accurately deter- 



