452 Forestry Quarterly 



Traverse Lines. — Sometimes it is impossible to locate sufficient 

 control points by triangulation. This most often happens in nar- 

 row canyons or canyons which are heavily timbered. In cases 

 of this kind, or where the accurate location is necessary, a tra- 

 verse line may be run. The telescopic alidade allows the use of 

 the stadia rod. The best rod to use is one which may be made 

 locally as described in "Plane Surveying," by Tracy. Tied to a 

 triangulation point, such a traverse line can be used as a sec- 

 ondary base. Their location is most frequently in the bottom 

 of the canyon unless the chief use is as a secondary base. For 

 secondary locations, a paced traverse line is often practical for 

 points of slight importance and whjere frequent checks are 

 possible. 



Use of Photographs. — A set of good pictures is a valuable sup- 

 plement to a map. Even with a film kodak, it is possible to get 

 pictures which will join nicely at the edges, and represent a wide 

 range of country in a panorama. Such pictures show the nature 

 of the cover, and to a considerable extent, the topography. 

 Trails, grazing allotment boundaries, etc., can be pointed out to 

 anyone unfamiliar with the country. A careful selection of 

 points from which these are taken will give photographs of 

 practically all the country mapped. A photograph is a great help 

 in a readjustment of contour lines or in filling in when it is 

 impossible to sketch all contours in the field. 



Field Experiences and Methods. — Following are some experi- 

 ences and outline of methods whose value has been proven in 

 the field. Some new methods which might be useful are also 

 mentioned. 



If the alidade is in adjustment, there is no need of turning the 

 telescope in the collar to take a check reading, as the slight cor- 

 rection possible could not be platted. Considerable care needs to 

 be taken in drawing the lines and handling the needle points. 

 Errors are much more apt to be accumulated through faulty 

 platting of the lines than through instrument errors. It is found 

 impractical to try to take the sights on this work without using 

 a very fine needle point in the board as a pivot. If the needle 

 is used once, it should be used constantly, one of the smallest 

 size, taking great care to set it in the board the same distance 

 each time and perpendicular to the plane of the paper. The 

 lines may be drawn from the needle center parallel to the blade. 



