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Measurements Used in the Original Surveys Done in Iowa


One Rod  

16.5 Feet  (or 25 Links)

Two Pole Chain   33 Feet  (or 50 Links)
Four Pole Chain   66 Feet  (or 100 Links)
Surveyor's Chain   66 Feet  (or 100 Links)
One Link   0.66 Feet
1/4 Mile   1320 Feet (or 20 Chains or 80 Rods)
1/2 Mile   2640 Feet (or 40 Chains or 160 Rods)
One Mile   5280 Feet (or 80 Chains or 320 Rods)
1/4 Section   160 Acres
1/2 Section   320 Acres
One Section   640 Acres (or one Square Mile)
One Township   36 Sections, 6 Miles Square or 36 Square Miles


Iowa Survey Methods


The current system of surveying the public lands which consists of guide meridians and correction lines which make up the regular pattern of “24-mile tracts” is known to students of modern textbooks on surveying. It is not well known that this system was not always in effect. That system was first widely adopted with the publication of the Instructions of 1855, which grew out of the instructions for surveys in Oregon issues in 1850.  Almost all of Iowa had been surveyed before 1855.

Here is a brief description of the control system used by the Iowa surveyors, some as far back as 1832.

The intersection of the fifth principal meridian and the national base line is the origin of the rectangular coordinates (the zero north or zero south and zero east or zero west point) to which all public land surveys in Arkansas, Missouri, Iowa, North Dakota, and portions of Minnesota and South Dakota are referred. This point is about 70 miles east of Little Rock, Arkansas.

The starting point of the fifth principal meridian is at the junction of the Arkansas River with the Mississippi River. It enters the State of Missouri in township 21 north, crosses the Missouri River in township 44 north; passes 39 miles west of St. Louis; intersects the Mississippi River at township 53 north. It is discontinued at this point and does not resume until township 77 is reached, above the bend of the Mississippi River in Iowa. It terminates at its intersection with the Mississippi River in township 91 north.

The national base line runs west from the place where the St. Francis River enters the Mississippi River in Arkansas. It passes about four miles south of Little Rock, Arkansas.

Because the fifth principal meridian is not a continuous line it was necessary to cary the line upward through Iowa on an offset. This offset line was run between ranges 4 and 5 west from Iowa’s south boundary to the first correction line, between townships 78 and 79; thence east a calculated distance (four townships) to the fifth principal meridian.

Correction lines were projected at ten township intervals, as near as possible. Actually there are eleven townships between the base line and (Iowa) and the first correction line, and ten townships between the first and second correction line, and twelve townships between the second correction line and the Iowa-Minnesota border.

 Using the middle latitude for Iowa (about 42 degrees north) as a basis for calculation we find from tables of convergence, that the amount of convergence for two meridians six miles apart in meridianal distance of 60 miles, or ten townships, would be almost 6.5 chains or about 429 feet.

Provision was made for the convergence by making an excess of measurement on the correction lines. This excess was placed in the west half of section 31, the intention was that the placing of an excess on the correction line would reduce the deficiency in width at the next correction and that there would be some place between the two correction lines, preferably midway, there the width would be exactly six miles. The amount of this excess was two chains at first, and finally was increased to three chains.

The early instructions did not include provision for the running of guide meridians. This oversight was most likely due to the fact that in none of the surveys east of Iowa had the distance between principal meridians been more that 25 townships. So, two guide meridians were run, one between ranges 25 and 26, and the other between ranges 39 and 40. Neither of these range lines ran the entire width of the state.


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