﻿ Acres

Measuring land in Acres

When pressure on agricultural land was low, the measurement of areas of land could be qualitative rather than quantitative:

how many cattle will this area keep ?
how many bushels of corn can be harvested each year ?
how many stacks of hay can be saved each year ?

Taxation, settlement, overcrowding, and agricultural innovations such as rotation of crops, meant that more objective ways were devised to measure areas of land.

Chain Surveying

Long before the days of accurate measurement of angles, and long long before Global Positioning Systems, surveyors developed methods of calculating even irregular areas of land fairly accurately from linear measurements. These methods (chaining, triangulation and offsets) are well described in many books, and at:
http://www.orbitals.com/self/survey/index.html

Surveyors used a decimal number system, because:

(a) it was easier to record and calculate;
(b) it was independent of local units of measurement, which varied from place to place;
(c) it could easily be converted into local units when necessary.

This decimal system was based on the surveyors' principal tool, the surveying chain.
To enable sub-chain readings to be taken, a chain was divided into 100 links.

A square chain is an area 1 chain long by 1 chain wide (or an irregular shape of the same total area).
10 square chains is an acre (a previously-existing word, here defined for surveying purposes).

By using an appropriate chain, a surveyor could present his results in acres of any size.
There were many different sizes of acre:

 Chain (yards) Link (inches) Acre (sq yards) Name 22 7.92 4840 Statute 24.8 8.928 6150.4 Scottish 25 9 6250 Cunningham 26 9.36 6760 Westmorland 28 10.08 7840 Irish or Plantation 32 11.52 10240 Cheshire