Civil Engineering Reference
In-Depth Information
parallel north will be less than 24 miles. That is why it is labeled “24 miles less
convergence”.
The same situation exists for the first standard parallel south. The township
boundaries along this parallel will be 24 miles. However, when the base line is
reached, convergence will cause the dimension of the quadrangle to be less than
24 miles. Notice in Fig.
7.3
that the range lines of the two abutting quadrangles do
not intersect at the base line. The township widths immediately south of the base-
line are less than those which are north of the baseline. This convergence becomes
important when we work with sections.
7.5 Sections
After the townships were created, each was divided into 36
Sections
. A section
is one mile square—at least some of them are. Each section contains 640 acres.
Figure
7.4
shows a township divided into sections.
The convergence of the range lines, which fix the township boundaries, makes
it impossible to create 36 sections which are exactly square. This is a common
problem in surveying. It occurs when a two dimensional plane must be fitted
to a spherical earth. There are a number of ways this problem might have been
solved. One way would have been to alter the shape of each township so that 36
of them would fit exactly in a township. However, this would make surveying dif-
ficult as the sections would no longer be squares. Another way to deal with the
Fig. 7.4
A township divided
into 36 sections. Sections
outlined in
red
are one mile
square. Sections on the
north and west boundaries
are subject to dimensional
changes resulting from
convergence
