2nd method. Lay off 100 yards; ascertain how many of your paces are necessary to cover this distance; multiply R. F. by 7,200,000, and divide by the number of paces you take in going 100 yards. The result will be the length of line in inches which will show 2000 of your paces.
3rd method. Construct a scale of convenient length, about 6 inches, as described in [Par. 1863], to read in the units you intend to measure your distance with (your stride, pace, stride of a horse, etc.), to the scale on which you intend to make your sketch.
For example, suppose your stride is 66 inches long (33 inch pace) and you wish to make a sketch on a scale of 3 inches = 1 mile. The R. F. of this scale is 3 inches/1 mile = 3 inches/63360 inches = 1/21120. That is 1 inch on your sketch is to represent 21120 inches on the ground. As you intend to measure your ground distances by counting your strides of 66 inches length, 1 inch on the sketch will represent as many of your strides on the ground as 66 is contained into 21120 = 320 strides. For convenience in sketching you wish to make your scale about 6 inches long. Since 1 inch represents 320 strides, 6 inches will represent 6 × 320 = 1,920 strides. As this is an odd number, difficult to divide into convenient subdivisions of hundreds, fifties, etc., construct your scale to represent 2,000 strides, which will give it a length slightly in excess of 6 inches—6.25. Lay off this length and divide it into ten main divisions of 200 strides each, and subdivide these into 50 stride divisions as explained in [Par. 1862].
[1889]. Position sketching. The following are the instruments used in position sketching:
- Drawing board with attached compass ([Fig. 2]);
- Loose ruler, on board ([Fig. 2]);
- Rough tripod or camera tripod;
- Scale of M. D.'s (shown on ruler, [Fig. 2]);
- Scale of sketchers, strides or paces (at six inches to one mile), on ruler;
- Clinometer (not necessary if board has slope board, [Fig. 6]);
- Scale of hundreds of yards shown on ruler;
- Scale of paces.
Methods to be used
(1) Select a base line,—that is, a central line 1/4 to 1/2 mile long in the area to be sketched. It should have at its ends some plainly marked objects, such as telegraph poles, trees, corners of buildings, etc., and from its ends, and intermediate points, a good view of the area should be possible. The base line selected should be capable of being measured.
(2) Set up, level and orient the drawing board at one end of the base (A), [Fig. 1], Y, for example. Draw a meridian on the sheet parallel to the position of the magnetic needle. Assume a point (A), [Fig. 1], Y, corresponding to the ground point (A), 890, on the sheet, in such a position that the area to be sketched will lie on the sheet.
(3) Sight at hilltops, stream junctures, stream heads, etc., to begin the locations of these points by intersection, labelling each ray so as to be able to identify it later.
(4) Traverse to (b) and complete the locations by intersection as previously explained. If the base line is not accurately measured, the map will be correct within itself in all of its proportions, but its scale will not necessarily be the scale desired.