What is a survey?

A survey is a method used to determine the relative positions of various objects on the land by measuring the horizontal distances between them. Briefly, a survey is a process of accumulation of data of various details related to land. The main objective of surveying land is to prepare maps to a suitable scale. Various types of maps such as topographical maps, cadastral maps, engineering maps, military maps, contour maps, geological maps, archaeological maps, and so on can be prepared by surveying.

Types of survey

Primarily, there are two types of surveys done:

1. Plane survey
2. Geodetic survey

Plane survey

In plane surveying, the curvature of the earth is neglected and the earth is assumed to be plane. Hence, a line joining any two points is considered as straight in this type of survey. In this survey, triangles are formed by joining any three points on the land. The triangles formed using this survey are considered to be plane triangles and the angles formed are considered as plane angles. Plane surveys are done for a very small area, generally less than 250 km².

Geodetic survey

In geodetic surveying, the curvature of the earth is taken into consideration. In this survey, the lines formed are considered as curved lines. The triangles formed by joining any three points on the land are considered to be spherical triangles and the angles formed are considered as curved angles. Geodetic surveys are done for large areas, generally more than 250km².

Land surveys are further classified into:

1. Topographical survey
2. Boundary survey
3. City survey
4. Engineering survey
5. ALTA survey

Topographical survey

A topographical survey is done to locate all the natural and manmade features of a region and prepare maps of the same to a suitable scale.

Boundary survey

A boundary survey, often known as a cadastral survey is done to determine the boundaries of fields, estate, houses, and so on. A boundary survey is crucial before initiating any type of construction to avoid any type of dispute.

City survey

A city survey is done to detect the premises, streets, water supply, sanitary systems, sewage system, and many other features of a city.

Engineering survey

An engineering survey is done to prepare a comprehensive drawing of the projects of roads, railways, tunnels, bridges, buildings, and many other engineering projects.

ALTA survey

ALTA stands for American Land Title Association. The ALTA survey is not mandatory but it is preferably conducted while buying or selling a real estate property. In this type of survey, all the existing features, improvement of property, utilities, and characteristics of land are surveyed and observed in detail.

Public Land Survey System (PLSS)

The Public Land Survey System is a primary surveying method used in the United States. Previously known as Rectangular Survey System, the PLSS was authorized by the US government under the Land Ordinance Act of 1785. The Seven Ranges in Ohio was the first land to be surveyed as per the Public Land Survey System.

From the year 1796 till the year 1836, the PLSS was used by surveyors under the jurisdiction of the office of the US Surveyor General. In the year 1836, the office of the US Surveyor General was placed under the jurisdiction of the General Land Office and GLO became the chief authority to look after the PLSS. Later, the office of the US Surveyor General and the General Land Office were eradicated in the years 1925 and 1946 respectively. In the year 1946, the Bureau of Land Management (BLM) succeeded the GLO. From the year 1946, the Bureau of Land Management is the governing body of the surveys, sale, and setting of lands in the United States. Now, in the United States, all the surveyors carry out surveys as per the Public Land Survey System under the jurisdiction of the Bureau of Land Management. Before Public Land Survey System, Metes and Bounds survey system was used in the United States. All the previous colonies of the 16^th century that were obtained as land grants were surveyed using metes and bound systems. The metes and bounds system uses the physical features of the local environment, such as trees, stones, walls, roads, streams, and so on to plot any land. The difficulty in this method is that the plots formed are of irregular shapes and it becomes difficult to describe the details of the land. Another difficulty in this system is that, as time passes, the natural features get faded, such as trees die, soils and rocks get eroded, streams change path, and so on. Hence, the chances of creating disputes increases. So PLSS, which is a coordinate system is used as the primary surveying method in the United States.

Procedure for surveying using PLSS

• On land, two survey lines are plotted from an initial point. One baseline runs east-west and another principal meridian line that runs north-south. A chainman is assigned to accurately measure distances and a compass man is also assigned to establish correct bearing at the placement of each chain. Next, latitudes are drawn parallel to the baseline at fixed standard intervals. The chainage or distances are written manually overbearing trees nearby the point.
• The land is divided into Survey Townships of approximately 36 square miles (93 km²) on each side with the help of township line and range lines. Township line runs east-west and range lines run north-south, at an interval of 6 miles (9.656 km) each.
• Finally, the township is divided into 36 sections of approximately 1 square mile (2.6 km²), each having each side nearly equal to 6 miles (9.656 km) and further divided into 4 subsections of approximately 0.25 square miles (0.65 km²) each.
• Due to the curvature of the earth, it becomes practically impossible to form every section of exactly 2.6 km². To reduce the error, all the range lines and half of all the section lines are plotted concerning the true north or the geodetic north of the earth.
• This division of the land up to sub-sections is carried out by the federal government. The rest detailed surveys are carried out by the surveyors or contractors after the sale of the plot. The contract of the survey of the plot is given to the deputy surveyor or contractor by competitive bidding.

Survey township

A survey township as per the PLSS is an area of 36 square miles, which is approximately 93km². A survey township is located by the principal meridian and baseline. If a system says Township 2 South Range 1 West, then it states that it is 1^st township to the west of prime meridian and 2^nd township to the south of the baseline. All the current township lines in the United States were surveyed by the US General Land Office in the past and were subdivided into smaller section lines by the private surveyors. All the boundaries of a township are marked on the U.S. Geological Survey topographic maps and are sold as per its reference. The images below show the difference between a road network in a PLSS system and non-PLSS system.

Context and Applications

The survey of public lands is useful for the students who are undertaking the following courses:

• Bachelors in Civil Engineering
• Masters in Civil Engineering
• Masters in Building Surveying

Practice Problems

1. Which survey is done to locate the natural or manmade features of a region?

1. City survey
2. Engineering survey
3. Topographical survey
4. Boundary survey

Answer: Option c

Explanation: Topographical survey is done to locate the natural or manmade features of a region.

2. Which survey can be done to locate the sewage system of a city?

1. City survey
2. Engineering survey
3. Topographical survey
4. Boundary survey

Answer: Option a

Explanation: City survey can be done to locate the sewage system of a city.

3. The PLSS was authorized by the US government under which law?

1. Land Ordinance Law
2. Land Survey Law
3. Public Land Surveys Law
4. None of the Above

Answer: Option a

Explanation: The PLSS was authorized by the US government under Land Ordinance Law.

4. In which year did the BLM succeed the GLO?

1. 1796
2. 1836
3. 1946
4. 1956

Answer: Option c

Explanation: The BLM succeeded the GLO in the year 1946.

5. In which direction does the baseline run as per PLSS?

1. East-west
2. North-south
3. Southeast-northwest
4. Northeast-southwest

Answer: Option a

Explanation: The baseline runs in the east-west direction as per PLSS.