Community Assistance

 

Surveying and Mapping Recommendations

BACKGROUND

 

Since its inception in 1960, the Commission has recognized the need for accurate base maps to conduct not only a sound regional planning program, but to support sound county and local planning programs as well. Accurate base maps depict the shape of the surface of the land and the precise location of its physical features, both natural and manmade. More specifically, information is required on relief; on the location of such natural features as lakes, streams, watercourses, drainage divides, and marshes and wetlands; on the location and extent of such manmade features as highways, railroads, airfields, and canals and drainage ditches; and on the location and orientation of real property boundary lines. For an area as large as the seven-county southeastern Wisconsin Region, such base maps must be constructed on map projections which recognize the curvature of the earth’s surface and permit distances and areas to be accurately portrayed and measured. Adequate maps of this type were lacking for the Region and its counties in the early 1960s.

To address this void, the Commission prepared and maintains current general purpose base maps of the entire Region, and for subareas of the Region such as watersheds. In addition to such general purpose base maps, the Commission has long recommended that for more definitive planning at the county and local levels of government, maps with a higher degree of accuracy and precision than required for regional planning be prepared and maintained current. To be effective for planning and engineering purposes, such maps must permit the accurate correlation of property boundary line information with topographic data.

Any accurate mapping project requires the establishment of a basic system of survey control. This control consists of a framework of points whose horizontal and vertical positions and interrelationships have been accurately established by field surveys. Map details are adjusted to, and mapping checked against, these known points. In addition to permitting the accurate correlation of property boundary line information with topographic data, the control network must be permanently monumented on the ground so that lines established on the map during planning and engineering may be accurately reestablished on the ground.

Toward this end, the Commission recommended in 1964 that all planning base maps be prepared by photogrammetric methods using a then unique system of horizontal control based upon both the U.S. Public Land Survey System, a property-orientated legal system based on field monuments, and the State Plane Coordinate System, a scientific system for accurate topographic mapping and engineering surveying. This control system would require relocating and permanently monumenting all section and quarter-section corners in the Region, and the utilization of these corners in the establishment of a field survey network tied to the North American Datum of 1927 (NAD 27) through the Wisconsin State Plane Coordinate System. This control system establishes the exact lengths and true bearings of all quarter section lines, as well as the geographic position—expressed in State Plane Coordinates—of the public land survey corner monuments. This horizontal control network provides the basis for subsequent topographic and cadastral (real property boundary) mapping. A further recommendation was made to determine the vertical position of each public land survey corner monument, as well as at least one attendant stable benchmark, using the National Geodetic Vertical Datum of 1929 (NGVD 29). This system of vertical control points would ensure that surveyors and engineers would have a known point of elevation on the NGVD 29 within about one-quarter mile of any point in the Region.

 

IMPLEMENTATION PROGRESS

 

The Commission has worked continuously with its county and local governments to implement the foregoing survey control and mapping recommendations. This includes:

  • Control Surveys

    The conduct of field surveys to enhance each monument as a station of known horizontal and vertical positions on both the U.S. Public Land Survey System and the State Plane Coordinate System, together with documentation of the entire survey control network. That documentation consists of control station (dossier) sheets and Control Survey Summary Diagrams (CSSDs). A dossier sheet is a record of a USPLSS control station, generally a section corner, quarter-section corner, center of section, or witness corner. Each sheet contains an identification of the corner, a sketch of the location, witness monuments and ties, monument coordinates and elevations, and other surveyor's information. CSSDs summarize horizontal and vertical control survey information obtained from the high-order control surveys carried out within the Southeastern Wisconsin Region. Each Control Survey Summary Diagram covers six USPLSS sections and shows the location and type of corner monuments; coordinates and elevations of the located corners; and grid distances, bearings, and interior angles of all USPLSS section and quarter-section lines

While the foregoing base mapping and related control survey recommendations were advanced in the age of hard copy mapping products, the recommended approach to surveying and mapping provided a sound basis in the subsequent digital age for the creation by county and local governments in the Region of automated parcel-based land information systems and automated public works management systems.

 

DATUM TRANSFORMATIONS

 

The Commission-recommended horizontal control survey network within the Region is referenced to the North American Datum of 1927 (NAD 27), a datum based upon the Clarke Spheroid of 1866, a spheroid which fits the North American Continent and the Southeastern Wisconsin Region well. The Commission-recommended vertical control survey network within the Region is referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29), a datum formerly known as the Sea Level Datum of 1929. In 1973 the Federal Government undertook a readjustment of the national horizontal control survey network, and adopted a new horizontal datum known as the North American Datum of 1983 (NAD 83), utilizing a new reference spheroid known as the Geographic Reference System of 1980. In 1977, the Federal government undertook a readjustment of the national vertical control survey network and adopted a new vertical datum, known as the North American Vertical Datum of 1988 (NAVD 88). The use of these new datums within the Region does not provide any significant advantages over the continued use of the Commission-recommended datums. Since no substantial benefits can be shown to occur from the use of the new datums and since a change in datums would incur very high costs, the Commission continues to recommend utilization of the older datums as a basis for surveying and mapping operations within the Region.

In order to facilitate the use of the new datums within the Region by such agencies as may determine to do so, the Commission, in July 1993 and October 1994, entered into agreements with a consulting geodetic engineer for development of operational computation systems that would permit the ready and reliable bidirectional transformation of coordinates between the two horizontal and two vertical datums concerned. The computational systems were documented in SEWRPC Technical Report No. 34, A Mathematical Relationship Between NAD27 and NAD83(91) State Plane Coordinates in Southeastern Wisconsin, December 1994; and SEWRPC Technical Report No. 35, Vertical Datum Differences in Southeastern Wisconsin, December 1995. Time has proven the computational systems documented in these reports to be sound and useful for their intended purposes.

Further changes in surveying technology since 1993 caused the Commission in 2008 to undertake a further review and evaluation of the Commission-recommended control survey program and the Commission role in that program. These changes have included, among others, the adjustment of the once “new” Federal datums to create NAD 83 (2007) and NAVD 88 (2007); the use of global positioning system (GPS) technology for both horizontal and vertical positioning; and the provision of a continuously operating reference station (CORS) network within the Region by the Wisconsin Department of Transportation to facilitate the use of GPS technology. These changes, and particularly the ability of GPS technology to accurately locate coordinate positions, led the Commission to create a Technical Advisory Committee of knowledgeable users of the recommended regional control survey system and asked that the Committee: 1) critically review and evaluate the continued utility of the Commission-recommended control survey system network; 2) recommend any needed changes in the network and the means for its perpetuation and use; and 3) recommend the Commission role, if any, in such perpetuation.

The findings and recommendations of the Technical Advisory Committee are set forth in SEWRPC Technical Report No. 45, Technical Review and Reevaluation of the Regional Control Survey Program in Southeastern Wisconsin, March 2008. These findings and recommendations are as follows:

  1. The Commission, its constituent counties and municipalities, and such special purpose governmental agencies as the Milwaukee Metropolitan Sewerage District should continue to utilize NAD 27 and NGVD 29 as a basis for horizontal and vertical survey operations within the Region, including land and public works related survey operations.
  2. The Commission, in cooperation with its constituents counties, should continue to maintain the network of monuments that perpetuate the U.S. Public Land Survey System and the attendant horizontal and vertical control survey networks within the Region; and
  3. The Commission should undertake the development of new equations for the bidirectional transformation of State Plane Coordinates between NAD 27 and NAD 83 (2007), and orthometric elevations between NGVD 29 and NAVD 88 (2007).

In accordance with these recommendations, the Commission in May 2008 entered into a contract with the consulting geodetic engineer for developing the desired new bidirectional transformation equations. The development of the equations was to be conducted in two phases as recommended in the SEWRPC Technical Report No. 45. Phase I was to consist of the development, test, and validation of a conceptual approach to the work, and was to include an application of the conceptual approach to a small sub-area of the Region. The Phase I work was also to identify any additional geodetic survey measurements that might be required in support of the development work. Phase I was completed in 2008. In addition to describing a proposed conceptual approach to the development of  the desired bidirectional transformation equations, Phase I recommended the conduct of certain additional geodetic field surveys within the Region to accurately correlate the old and new datums; to provide validation of the accuracy of the transformed values; and to demonstrate the practicality of the use of GPS technology with both the old and new datums and the CORS network established within the Region by the Wisconsin Department of Transportation (WisDOT).

Phase II consisted of the actual development of the desired bidirectional transformation equations; the conduct of necessary additional geodetic survey work within the Region; and the demonstration of the practicality of utilizing GPS technology with the Continuously Operating Reference Stations (CORS) network newly established within the Region by the Wisconsin Department of Transportation. Phase II also included—for 100 selected monumented U.S. Public Land Survey corners—a comparison of coordinate and elevation values as determined by application of the bidirectional transformation equations and as determined by high-order field surveys. The transformed coordinate and elevation values were then assessed to determine the ability of the bidirectional transformation equations to meet National Map Accuracy Standards. To facilitate application of the equations, the Region was divided into 17 sub-areas with each area assigned a confidence level—A, B, or C—indicating the level of accuracy that could be expected in applications of the bidirectional transformation equations. Phase II was completed in 2010, and the findings and recommendations reported in SEWRPC Technical Report, No. 49, Bidirectional Transformation of Legacy and Current Survey Control Data within Southeastern Wisconsin, May 2010.

 

COST ESTIMATE TO CONVERT TO NEWER DATUMS

 

In spite of the rationale advanced by the Commission for the continued use of the legacy datums within the Region, questions continue to be raised by some practicing surveyors and land information system managers as to why the Commission continues to use, and recommends the continued use by others of, the legacy datums within the Region. In response to these questions, the Commission engaged the firm of Aero-Metric, Inc. to prepare an estimate of the cost that may be reasonably expected to be incurred in a resurvey of the existing control survey network within the Region in order to base that network upon the new datums introduced by the Federal government. The cost estimate so prepared is included in SEWRPC Memorandum Report No. 206, Estimate of the Costs of Converting the Foundational Elements of the Land Information and Public Works Managements Systems in Southeastern Wisconsin from Legacy to New Datums, October 2012. The cost of such a resurvey, if carried out over a five-year period, was estimated at $7.16 million.

The resurvey would provide only two of the four foundational elements of a sound parcel-based land information or public works management system; namely: 1) a map projection and related datum; and 2) a survey control network that manifests the projection and datum on the surface of the earth. The resurvey would place these two elements on the new NAD 83 (2007) datum and would do so with at least as high an accuracy level than the legacy control survey network within the Region. Two additional foundational elements would, however, also have to be transformed to fit the new datum; namely: 1) large-scale topographic maps meeting National Map Accuracy Standards; and 2) matching large-scale cadastral maps meeting a comparable level of accuracy. The cost of preparing the new topographic maps over a five-year period is estimated at about $26.56 million. The cost of preparing the new cadastral maps over a five-year period is estimated at approximately $8.84 million, bringing the total cost of providing the four foundational elements, to the same or higher quality as the elements provided for the legacy systems, to approximately $42.56 million. By substituting less desirable orthophotographs for the topographic maps, this total cost could be reduced to about $21.08 million, or by about 50 percent.

The foregoing substantial cost entailed in providing new foundational elements would not include the cost of transforming the attribute data presently contained within the land information and public works management systems developed within the Region from the legacy to the new datums. Such transformations would be possible through application of the bidirectional transformation equations developed by the Commission, or by the application of commercially available software programs. The use of such transformation methodologies might also be considered to provide the two base map elements of the four foundational elements described above. The transformed base maps, however, may not meet National Map Accuracy Standards for the topographic maps, nor the compatible accuracy standards for the cadastral maps, thus, destroying the integrity of the four foundational elements provided by the legacy systems.

It is unlikely at this time that funding of the costs associated with a datum transformation within the Region could be obtained. Even if such funding could be obtained, however, a transformation would not necessarily be in the public interest. Good public administration practice requires that it be shown that the benefits derived from a potential investment exceed the costs entailed. To date, none of the proponents of a datum transformation within the Region have provided evidence of any significant monetary benefits that might accrue from the transformation. Consequently, the Commission decision to continue to use the legacy datums within the Region, and to recommend the continued use of those datums to the county, municipal,  and special purpose government agencies operating within the Region, remains sound and in the public interest.

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Southeastern Wisconsin Regional Planning Commission

 

W239 N1812 Rockwood Drive
P.O. Box 1607
Waukesha, WI 53187-1607

 

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Phone: (262) 547-6721
Fax: (262) 547-1103
E-mail: sewrpc@sewrpc.org

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