Surveys are conducted to satisfy a range of needs. As a result, the equipment and techniques used vary from one type of survey to another.
Geodetic surveys establish precise horizontal and vertical positions of reference monuments over large areas. Three dimensional mathematics are used to compensate for earth curvature.
Mapping surveys are made to determine the locations of natural and cultural features, and to define the configuration (relief) of the earth's surface. This work may be done on the ground or from aerial images. Property surveys are a specialized form of mapping
survey used to locate land ownership boundaries and marked corners, plus
features and improvements on the property.
Geodetic Surveys
The highly stable, ground reference monuments established by geodetic surveys serve as a framework for Geographic and Land Information Systems (GIS/LIS). They also provide reference control for mapping and aerial photography projects, and are the measurement and positional foundation for engineering planning, design and construction. Geodetic surveys have been conducted in the United States for nearly 200 years. Hundreds-of-thousands of monuments have been placed nationwide, with nearly 20,000 in Wisconsin alone. Traditionally, geodetic surveys have been divided into two types, horizontal and vertical.
Horizontal surveys establish geodetic latitudes and longitudes of monuments with reference to a mathematical surface called an ellipsoid. Horizontal surveying measurements are made on the surface of the earth, but computations are performed in a coordinate system referenced to the ellipsoid, as though the measurements were made there.
Typical horizontal coordinate systems based on these measured values are the plane rectangular coordinates in the State Plane System, Universal Transverse Mercator, Wisconsin Transverse Mercator, or the Wisconsin County Coordinate System. Today, horizontal control field survey procedures are conducted using GPS due to its ease of use, speed and extremely high accuracy capabilities over long distances.
Vertical surveys establish heights/elevations of positions for a network of monuments often referred to as bench marks. The elevations are referenced to a surface of constant gravitational force called a geoid. The geoid is not physically real, but can be thought of as the surface formed if the oceans were free to flow and adjust to the combined effects of the forces of gravity and the earth's rotation. This is equivalent to sea level without any continents - a surface of equal gravity.
Depending on accuracy requirements, vertical surveys have been traditionally run by either differential leveling or trigonometric leveling. GPS can also be used to establish vertical control, but the most accurate and widely applied method is precise differential leveling.
Control points established by geodetic surveys will have a horizontal position or an elevation, but usually not both, since horizontal and vertical positions are developed by different methods and with respect to the different reference surfaces described above. Separation of the two networks was the norm prior to widespread use of GPS, since horizontal networks were measured from hilltop to hilltop while vertical networks followed railroads and highways which had been routed to avoid hills.
By contrast, the current Height Modernization Project uses common monuments for both horizontal and vertical geodetic control.
Return to TopMapping Surveys
Mapping surveys are done to identify the location of the earth's features, both natural and cultural. Once the size, shape and location of these features are determined they can be represented on maps. Natural features shown on maps may include drainage features such as river, streams, lakes and ponds; vegetation; and the shape of hills, valleys, and submerged lands. Cultural features are those items produced by people, and include roads, railroads, buildings, bridges, towers etc.
Mapping surveys collect information in one of two basic ways, either remotely through the use of aerial photography or satellite imagery, or by ground measurement techniques. Ground-based methods traditionally involve the measuring of angles and distances -- for instance to map the boundary of a piece of land (usually called a "parcel"). Equipment to accomplish this work has evolved over time. To determine distance, chains and steel tapes have given way to the electronic distance meter (EDM). For angles, the theodolite replaced more primitive telescopic devices. The "total station" incorporates both distance as well as angular measurement devices.
Survey-grade GPS equipment can indirectly yield both high-accuracy distance and angle bearing between points. A less accurate but still valuable use of GPS is to follow a path (e.g., the boundary of a wetland) to collect a stream of points that can be mapped. This technique typically uses resource-grade GPS equipment.
Mapping of features from aerial imagery is most often based on the principles of photogrammetry (the well-established science of making measurements from photographs). Photogrammetry is economical, accurate and used on most all mapping projects covering large areas. In contrast, ground surveys are used for preparing very large-scale (detailed) maps of small areas. Photogrammetry does require some use of ground survey to establish control, a means to accurately tie the map to known ground positions, and to field-check mapped features for accuracy.
Sometimes features are mapped directly from aerial photographs, typically two overlapping images viewed in stereo 3-D. An example is interpretation of wetland cover types. In some cases the photographs are first rectified (adjusted to minimize the effect of aircraft tilt) of converted to orthophotos.
In addition to specialized mapping cameras using film, other sensing instruments can be carried in aircraft or spacecraft. These include scanners sensitive to visible and near-visible wavelengths, and others used to detect thermal energy. Images from these remote-sensing devices can be interpreted visually in some cases or more often through various digital processing techniques to reveal a variety of phenomena. Devices to map terrain include radar and lidar (which sends pulses of light to the ground and measures the amount of light reflected back and the time of transit).
Property Surveys and Maps
A property survey describes, maps, and locates land ownership boundaries and corners, features and improvements. Property surveys must be performed by a Professional Land Surveyor who has been licensed by the Wisconsin Department of Regulation and Licensing. The surveyor assumes the roles of historian, law scholar, investigator and interpreter. The surveyor researches the property's history to correctly interpret its deed or legal description.
To learn more on when a property should be surveyed consult the Wisconsin Society of Land Surveyors.
Property Description Types
Land titles in Wisconsin are transferred by written documents called deeds, which contain a description of the property.
Property descriptions are prepared as the result of a land survey. A property description may combine two or more methods
of description:
- metes and bounds
- block-and-lot system
- township, section, subdivisions
- mapping coordinates
- plat review
This method of property description has a long history and is probably the most understandable to people unfamiliar with surveying methods and jargon. Essentially, the description follows a path around the perimeter of a piece of land, calling out a series of points (and the lines between them) that are related to each other by geometry. The starting place on the perimeter is called the Point of Beginning (POB) although the survey may be anchored to a Point of Commencement (POC) such as a nearby PLSS corner. The POB typically is marked by a monument or prominent physical feature, and other points along the described path may be similarly marked.
Here is a hypothetical example: Commencing at the West 1/4 corner of Section 13, Town 22 North, Range 3 East; thence North 80.00 degrees East 341.74 feet; thence South 18.22 degrees East 301.34 feet; thence...to the point of beginning.
Note that this description may be problematic since it does not provide
reference to which principal meridian the Town/Range/Section is related; it
might be confused with a similar section 13 in another state.
Block and Lot System
In urban areas, the most common way of describing land is as lots. Multiple
lots are numbered within blocks, tracts, or subdivisions. Maps of these groups
of lots are produced to show the layout of the lots and surrounding lands dedicated
to public uses such as streets.
Township, Section, and Small Subdivision
The Public Land Survey System provides the basis for describing many rural lands in Wisconsin.
An example is: West 80 acres of SE 1/4 of Sec. 33, T 19 N, R 2 W, 4th Principal Meridian.
An important point about such a description is that the remaining part of that quarter section will
not also be 80 acres (or at least 80.000 acres) because the full quarter section will never be exactly
160 acres. In other words, a separate parcel described as the East 80 acres might overlap the West 80
acres, or might leave some land of ambiguous ownership between the two 80-acres pieces so subdivided from
the full quarter section. A less ambiguous legal description would reference the "West half of
the SE 1/4" of the section; that would fit nicely if the other part of the subdivided quarter section
were described as the "East half."
Land can also be described purely in terms of coordinates, such as in a string of coordinates defining points along the boundary. This method provides an easy way to map a parcel but traditionally has been the most difficult for the public to understand. The emergence of low-priced GPS receivers has made it easier for people to use coordinate values as the means to navigate to points on the land, although the design limitations of such receivers precludes their use in locating parcel boundaries with anything more than rough accuracy. Plat Review
Chapter 236 of the Wisconsin Statutes establishes a process for reviewing subdivision plats. This function is managed by the Wis. Dept. of Administration. “The goals of Plat Review include promoting the orderly layout of land; facilitating adequate provisions for water, sewerage, road ingress and egress and public access to all navigable water; and certifying technical accuracy, retraceable boundaries and conveyancing by accurate legal description.” The Plat Review website includes a wide variety of material including the full Platting Manual. Local governments may also have programs to oversee the platting process.
As special kind of plat is the Assessors Plat which is a process by which an area of existing land parcels that suffer from conflicting or confusing legal descriptions can in effect be replatted.
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