A PLANE TABLE SKETCHING CASE. 

 By Wm. J. Padth. 



The usual method employed by the Forest Service in obtaining 

 topography when a topographic map is made in conjunction with 

 a timber reconnaissance is termed the strip system. Straight lines 

 are run through the territory to be mapped. The primary con- 

 trol is established accurately with standard surveying instruments 

 by base line crews. The secondary lines of control are run by one 

 man, the compassman. The compass is the instrument used, and 

 a standard form of compass has been adopted by the Forest Ser- 

 vice. 



Several forms of map sheet holders have been used, each type 

 designed to meet the requirements of the work peculiar to the 

 region where it was used. A map sheet holder fitted to meet the 

 requirements of all conditions must satisfy the following de- 

 mands : it must be light and strong. It cannot be bulky since it 

 must be portable. The compassman must run straight lines, and 

 small patches of dense underbrush will impede his progress, 

 hence the instrument should be equipped with carrying straps, 

 or raw-hide laces, so that it can be carried suspended from the 

 shoulder. This gives the compass-man the use of both hands- 

 It is of further advantage in sighting with the compass. 



Provision must be made in the construction of the map sheet 

 holder to furnish protection to the map sheets. Showers are 

 encountered during the day and going to and from the work. 

 A wet map sheet cannot be used satisfactorily. 



When only one map sheet is mounted, the unused sheets are 

 not subject to injury. The compass-man should be able to pro- 

 tect his clean sheets. Often two or three sections are being 

 worked the same day. When two sections are covered in one 

 strip the compass-man could mount the new sheet at the end of 

 the section. The map sheet holder must provide for a quick 

 changing of sheets without injury to the map sheets. Further, 

 the compass-man must have a map sheet holder equipped with a 

 separate water-proof, closed compartment for the reception of 

 the unused sheets. He must be able to preserve them flat and 



