448 Forestry Quarterly 



advantage cannot be had of triangulation points. The platting 

 of U. S. Geological Survey triangulation stations or bench marks 

 should be by means of latitudes and longitudes. The platting 

 of township plats may also be checked by the latitude and longi- 

 tude. In plane table triangulation, the table is always parallel to 

 its original position, so if at any time after the work is started, 

 a check is made by a solar or star observation, a true meridian 

 must be platted on the paper, making allowance for convergency 

 of meridians. Where any tie with other land office work is made 

 at a distance from where the work began, the layout must be 

 made with full allowance for convergency. 



Under any circumstances, and especially if there are U. S. Geo- 

 logical Survey triangulation stations within reach, it is a very 

 good plan to plat the area and the location of known points within 

 sight on a scale of one-half inch to the mile. If this sheet is 

 used while the triangulation progresses, a tie is made to a consid- 

 erable area outside that actually mapped, and new points located. 

 This small scale map is particularly valuable in assembling the 

 results with relation to the other outside country, a part of which 

 is generally surveyed. 



Planning field Work. — As far as possible, the units on the 

 field sheets should include water basins or other natural units. 

 It is very necessary for accurate work to have a good system 

 of signals distributed over the area. It is possible to set these 

 signals from each camp before the mapping begins from that 

 particular camp, but the better way is to have the signals all set 

 before commencing the triangulation. This is especially true if 

 the instrument man is not very familiar with the country. The 

 preliminary work in setting signals gives him the opportunity 

 to plan the work ahead and know from what points he can accom- 

 plish the most, also which points he will locate with the greatest 

 possible accuracy. The signals may be set at the time of making 

 the preliminary examination of the area. Since this work will 

 be used as a basis for grazing and timber reconnaissance, it is 

 desirable to locate as many points as possible which can be used 

 to tie in later work. For this reason, more signals will be set 

 and monuments made than would be necessary for reasons of 

 control alone. In our case, one signal with monument of rocks 

 was made on the average for about every two square miles. 



