Surveying Units and Terms

Units of Measure

• Acre - The (English) acre is a unit of area equal to 43560 square feet, or 10 square chains, or 160 square poles.
• A square mile is 640 acres. The Scottish acre is 1.27 English acres.
• Arpent - Unit of length and area used in France, Louisiana, and Canada. As a unit of length, approximately 191.8 feet. The (square) arpent is a unit of area, approximately .85 acres.
• Chain - Unit of length usually understood to be Gunter's chain, but possibly variant by locale. Chains equal to one half the standard length are found in Virginia. The name comes from the heavy metal chain of 100 links that was used by surveyors to measure property bounds.
• Gunter's Chain - Unit of length equal to 66 feet, or 4 poles. A mile is 80 chains.
• Hectare - Metric unit of area equal to 10,000 square meters, or 2.471 acres.
• Hide - Old English unit of area usually equal to 120 acres.
• Labor - The labor is a unit of area used in Mexico and Texas. In Texas it equals 177.14 acres (or 1 million square varas).
• League (legua) - Unit of area used in the southwest U.S., equal to 25 labors, or 4428 acres (Texas), or 4439 acres (California).
• Link - Unit of length equal to 1/100 chain (7.92 inches).
• Perch - See pole
• Pole - Unit of length and area. Also known as a perch or rod. As a unit of length, equal to 16.5 feet. As a unit of area, equal to a square with sides one pole long. An acre is 160 square poles. It was common to see an area referred to as "87 acres, 112 poles", meaning 87 and 112/160 acres.
• Rod - See pole
• Rood - Unit of area usually equal to 1/4 acre.
• Vara - Unit of length (the "Spanish yard") used in the southwest. The vara is used throughout the Spanish speaking world and has values around 33 inches, depending on locale. The legal value in Texas was set to 33 1/3 inches early this century.

Surveying Terms

• Call - Any feature, landmark, or measurement called out in a survey. For example, "two white oaks next to the creek" is a call.
• Chain carrier - An assistant to the surveyor, the chain carriers moved the surveying chain from one location to another under the direction of the surveyor. This was a position of some responsibility, and the chain carriers took an oath as "sworn chain carriers" that they would do their job properly.
• Condition - See Conditional line.
• Conditional line - An agreed line between neighbors that has not been surveyed.
• Corner - The beginning or end point of any survey line. The term corner does not imply the property was in any way square.
• Declination - The difference between magnetic north and geographic (true) north. Surveyors used a compass to determine the direction of survey lines. Compasses point to magnetic north, rather than true north. This declination error is measured in degrees, and can range from a few degrees to ten degrees or more. Surveyors may have been instructed to correct their surveys by a particular declination value. The value of declination at any point on the earth is constantly changing because the location of geographic north is drifting.
• First station - See Point of Beginning
• Gore - A thin triangular piece of land, the boundaries of which are defined by surveys of adjacent properties. Loosely, an overlap or gap between properties.
• Meander - "with the meanders of the stream" means the survey line follows the twists and turns of the stream.
• Out - An 'out' was ten chains. When counting out long lines, the chain carriers would put a stake at the end of a chain, move the chain and put a stake at the end, and so on until they ran "out" of ten stakes.
• Point of Beginning - The starting point of the survey
• Plat - A drawing of a parcel of land.

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