Captain Vetch on the Utility of Contour Lines cn Plans. 61 
tion is to apply the straight edge of a slip of paper on the 
line A B (on the plan) and to mark off on the first all the in- 
tersections of contour and other lines; this done, the slip of 
paper is next applied to the section lines A’ B’, to which the 
marks of intersection are transferred ; and from these marks 
so transferred, perpendicular lines are drawn to the line 
A'B, and the intersection of these last with the parallel 
lines of the section already drawn, as mentioned above, give 
the various heights on the section, and nothing further is re- 
quired than to join these points with lines, to give the out- 
line or profile of the ground, and all this may be done a 
hundred miles from the spot; but if no such contour map 
existed, the engineer would have to send a surveyor with 
instruments to level over the ground, and considerable delay 
and expense must be incurred. 
Again, suppose that it is wanted to lay down a new line 
of road from C to D, without recourse to a section, the con- 
tour lines would shew that the dotted line CD would be 
very direct, and would give the most gentle ascents and 
descents, and if it be required to know the amount of these, 
and the quantity of cutting and filling to reduce the line of 
a regular surface, and above the influence of floods, we have 
only to repeat, in regard to a section on the line C D, what 
has been said in respect to that on the line A B, from which 
will be shewn the cuttings and embankments necessary for 
our purpose ; the space between the dotted line, and the line 
of surface indicating the extent of each. 
If the contour lines on a plan give such facilities for lay- 
ing out common roads, these advantages will be still greater, 
in respect to laying out railways, canals, embankments, and 
water-conduits. 
What do you consider would be the expense of laying 
down these contour lines !—In conjunction (or rather prior 
in order) to the contouring, levellings will have to be made 
to determine with great accuracy the positive heights of a 
number of points within the town, as has been done by the 
Ordnance Survey in several towns, and while that process 
is going on, the contour lines can be added at little addi- 
tional expense. Thus at Leeds, over a space ‘containing 
