METHODS OF MAP MAKING 121 



method already not too accurate, to additional errors, and 

 should not be employed except when it is the only practi- 

 cable method. 



This method of survey may suffice in favorable condi- 

 tions, and where the requirements are not of the strictest. 

 Work with the level, however, is quick and sure, and in 

 general it will be found advisable to use it freely. 



The Map. In plotting tracts of this size, and up to a few 

 hundred acres in extent, scales of 400 feet or 20 rods to the 

 inch are found to go well with a 10-foot contour interval, 

 and to furnish a serviceable map. A larger scale and a 

 smaller contour interval would naturally go together. 



3. MAPPING LARGE TRACTS 



A. With Land already Subdivided. If the region to be 

 mapped comes under the public land surveys, or if there are 

 plain and reliable lines of other origin on the ground, a 

 skeleton of level lines with barometer work tied to them is 

 the treatment indicated. Generally the leyel work is best 

 carried along the waters or roads. Ponds and lakes form 

 the best sort of reference points, and frequently natural 

 water levels perform a large part of the work required. 

 Section lines may, however, furnish in some cases the best 

 routes available, while on very broken land it might be 

 necessary to resort to the vertical angle. 



How the barometer work shall be done depends on 

 circumstances. If the weather is perfectly steady, or the 

 level points are near enough together, elevations may be 

 read direct without a weather change correction. If, 

 however, the weather is shifting, and the cruiser must stay 

 away from known points many hours at a time, a station 

 barometer or barograph will have to be employed. In any 

 case, the topography can be mapped at the same time that 

 the timber is being examined. 



B. Topography Based on Survey of Roads or Streams. 

 If the tract to be surveyed is an undivided township, or is in 

 any other form that is too large for accurate mapping, it may 

 be cut up by one means or another into smaller areas that 

 can be handled. The lines of easy subdivision naturally 



