MAP PHdJEOTlOi^. 
61 
Modifications of the Conical Projection. 
When it is intended to represent any portion of a country situated ill 
high latitudes, it will he necessary, io prevent distortion, to make nse of 
the conical projection, or some modification of it; and if the area it is 
intended to include is of small extent, it will be desirable to draw tlffi 
map on a larger scale than when it is to comprise an extensive portion 
of the globe. In many cases it would be found that the centre from 
which the parallels would have to be described, according to the conical 
projection, would lie so far outside the extent of the map as to render 
it extremely inconvenient to describe the curves representing the parallels, 
when the following method should be adopted, by which this difficulty 
will be overcome. 
In the following example the projection includes an area comprised 
between the 50th and 56th degrees of north latitude, and from the 2nd 
to the 6th degree of west longitude. 
Having decided on the scale on which the map is to be drawn, con¬ 
struct a diagonal scale (see Fig. 2) in the following manner:— 
On a line equal to the length of one degree of latitude of the scale 
decided on, erect a perpendicular at each end, also equal to the length 
of one degree of latitude, and join these lints, thus forming a square, 
the sides of which are equal to one degree of latitude of the scale 
of the map. Next carefully divide each of the perpendiculars into 
six eciual parts, and join these by diagonal lines from 0 to 10, 10 to 
20, and so on, as shown (see Fig. 2). Next divide the lines at the 
top and bottom of the square into ten equal parts, and join them 
by parallel lines; these lines will then constitute decimal divisions of 
the diagonals, and any measure can now be taken from this scale which 
is not less than a sixtieth of the degree. 
Having constructed the diagonal scale, draw a base line, A B, near 
the bottom of the sheet of paper, and erect the perpendicular, C D, to 
represent the central meridian of the map, which in this case is 2° 
west longitude, and taking from the diagonal scale, with the compasses, 
the length of one degree of latitude, measure off six of these degrees 
from C towards D, leaving between the base line and the first a space 
equal to 10' of latitude for a small part of the country, which extends to 
