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SIY8.TXT
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SIY8.TXT Measure Acreage 45
Chapter 8
Measure Acreage
In this chapter, you will calculate the acreage of a property
from the map.
You will need:
a) These instructions,
b) Pencil & paper,
c) Common calculator, or hand arithmetic,
d) The maps which you plotted in Chapter 1.
You will NOT need:
a) To believe the seller's word.
The easiest method to use to measure acreage is to simply count
the squares. Yes, there are fancier ways to solve the problem.
Counting squares on a map has the advantages of simplicity and
ease. No magic.
Get out Graph 1, where you plotted your very first map from the
description in Table 1. Count the squares within the boundary
lines of your map. If a square is on the line, count it only if
more than half of it lies within the boundary.
Each square is 0.2 inches on a side. The area of each square is
the square of the side. 0.2 * 0.2 = 0.04 square inches in each
square. To find the area within the boundary, multiply the
number of squares within the boundary times the area of each
square. This is the area in square inches.
In computerese, the symbol for multiplication is "*", and the
symbol for division is "/". Since my printer prints in
computerese, whatcha see is what you got.
Check your answer. Is it reasonable? Is 413 square inches
within the boundary a reasonable value, or a blunder?
SIY8.TXT Measure Acreage 46
If this were the plot of an actual parcel of land plotted at the
scale of 100 feet per inch, then you could calculate the acreage
of the land represented. At 100 feet per inch, the side of each
square represents 20 feet on the ground. The area of each square
represents 20 * 20 = 400 square feet on the ground. There are
43,560 square feet in one acre. Divide the area represented by
one square on the map by the area of one acre, 400 / 43,560.
Thus each square on the map represents 0.0092 acres.
Now multiply the number of squares times the part of an acre
represented by each square. The result is the number of acres
inside of the boundary. I calculate 1.03 acres. There is an
error associated with this number. This error ranges from 1% to
10%, depending upon the quality of your survey.
Now try it with the map drawn from Table 2. You plotted this map
at a scale of 100 poles per inch. The side of each square
represents 20 poles on the ground. A pole is a rod is 16.5 feet,
so each side is 330 feet. The area of each square is 108,900
square feet, or 2.5 acres.
This parcel was bought as 140 acres. How many acres do you think
are there?
This method of the squares works at any scale. But you must
calculate a new number of acres per square each time that you
change either the scale of your map or the mesh of your graph
paper.
You should plot your map so that it covers hundreds of squares.
Smaller maps may have considerable error from squares on the
boundary. To check for blunders, mark out a square with sides of
209 feet on your map. This represents one acre.
What happens when there is an obvious closure error? Well,
you'll just have to fudge it. I usually just draw a line between
the closing stations and call that the boundary. If I think the
error is worth correcting, I draw a triangle across the map, with
one side of the triangle being the closure error. I then either
add or subtract the area of this triangle, depending upon whether
the closure error underlaps or overlaps.
A better way is to sketch a new version of the map with the error
distributed around the whole loop. If you have very much error
to correct, then you have blunder, not error. The cure is to go
back and survey it right the next time.
SIY8.TXT Measure Acreage 47
There are mathematical methods to distribute the closure error
and measure the acreage, but they require the use of a computer.
If you have access to a computer, then use my computer program
CAVEMAP1.EXE for the ibm pc.
Calculate the area of the plot of the description of Table 3.
The proper acreage is that calculated from the distances
corrected to horizontal with the clinometer and COS. The
uncorrected acreage will always be greater than the true
acreage. Perhaps the difference is enuf to be worth correcting.
You decide.
You will be amused to know that the legal standard for accuracy
of acreage for Kentucky surveyors is plus or minus 10%. If you
can't survey that well yourself, ask for your "dollars" back.
There are several other units used for the measurement of land.
The metric unit (used everywhere but the United States of
America) is the hectare. One hectare is 100 ares, or 2.47
acres. The are [pronounced "air"] is 100 square meters. A
square rod [or perch, or pole] is 272.25 square feet, or 0.00625
acre. A rood is 40 square perches, or a quarter acre. A section
in Township and Range territory is one square mile, 640 acres. A
quarter section is 160 acres. That assumes that the section is
not an irregular section.
The acre is 10 square chains, or 43560 square feet. That is,
unless you are speaking British. In that case, an acre is 4
roods, which is only 0.999997123 of the American acre or
43559.87471 USA square feet. If your land is so valuable that
this makes a difference, then you shouldn't be using the compass
and tape method of land surveying.
Copyright (c)1994 by David Perry Beiter
If you have any questions, problems, or comments, write or call
me. Dave Beiter, CAVE Inc, 1/2 Fast Road, Ritner KY 42639.
606/376-3137.
MCI Mail: 635-1762
byter@mcimail.com
X.400: c=US;a=MCI;s=BEITER;d=id=6351762
CIS: >MCIMAIL 635-1762 (be sure to include your name in the text)