PLOTTING

, in Surveying, the describing or laying down on paper, the several angles and lines, &c, of a tract of land, that has been surveyed and measured.

Plotting is usually performed by two instruments, the protractor and Plotting-scale; the former serving to lay off all the angles that have been measured and set down, and the latter all the measured lines. See these two instruments under their respective names.

Plotting Scale, a mathematical instrument chiefly used for the plotting of grounds in surveying, or setting off the lengths of the lines. It is either 6, 9, or 12 inches in length, and about an inch and half broad; being made either of box-wood, brass, ivory, or silver; those of ivory are the neatest.

This instrument contains various scales or divided lines, on both sides of it. On the one side are a number of plane scales, or scales of equal divisions, each of a different number to the inch; as also scales of chords, for laying down angles; and sometimes even the degrees of a circle marked on one edge, answering to a centre marked on the opposite edge, by which means it serves also as a protractor. On the other side are several diagonal scales, of different sizes, or different divisions to the inch; serving to take off lines expressed by numbers to three dimensions, as units, tens, and hundreds; as also a scale of divisions which are the 100th parts of a foot. But the most useful of all the lines that can be laid upon this instrument, though not always done, is a line or plane scale upon the two opposite edges, made thin for that purpose. This is a very useful line in surveying; for by laying the instrument down upon the paper, with its divided edge along a line upon which are to be laid off several distances, for the places of off-sets, &c; these distances are all transferred at once from the instrument to the line on the paper, by making small marks or points against the respective divisions on the edge of the scale. See fig. 2 & 3, plates xxi and xxii.

Plotting-Table, in Surveying, is used for a plane table, as improved by Mr. Beighton, who has obviated a good many inconveniencies attending the use of the common plane table. See Philos. Trans. numb. 461, sect. 1.