In the public sector, governments administer and make policy through the creation of and maintenance of land records that are associated with a parcel of land. Thus the parcel is often the basic administrative unit of local government. In Wisconsin, the Wisconsin Land Information Program (WLIP) has been a key source of funding facilitating ever more complete digital parcel mapping at the county level. Many Wisconsin counties have completed county-wide parcel mapping and are focused on continued maintenance and updating best practices around this valuable mapped layer of land tenure information.
As geospatial analysis and business analytics have grown, so too has the market for on-demand parcel information. As a result, there are several commercial efforts to gather and assemble regional, statewide or even nationwide parcel information. Recognizing this trend, many States have pursued statewide integration of parcel map information from local governments, providing a coordinated point of contact for providing consistent updates to 3rd party users of this information.
Parcel maps are developed at many levels of government and by the private sector. These maps help facilitate administration, zoning, building and site development, flood control, lake and stream erosion control, and the planning, design and construction of roads and public works. In the private sector, parcel maps are useful to attorneys, appraisers, assessors, surveyors, engineers, and utility corporations as a means to inventory land holdings and index land records.
Parcel maps are unique because they have no federal or state oversight with their development. Historically, most parcel maps have been developed at the local level, where content, procedures, methods, and standards widely vary. As a result, many types of parcel maps have been produced in order to meet a variety of purposes. The very definition of “parcel” or “parcel map” can be controversial and confusing.
As mentioned, parcel definitions vary depending on the application. Differences can be caused by factors including: attempts to represent separate parcels under the same ownership, existence of administrative boundaries, movement of natural features that define boundaries, changes in land tenure and land use, varying levels of interest in land, and status of publicly owned lands. These variations and multiple definitions can complicate data use and data sharing.
The most common parcel maps found today are local government tax parcel maps. Tax maps are used for locating and describing properties that are linked to owners, tax bills, and other assessment information. Because of these needs, tax maps typically represent a generalized portrayal of parcel locations and dimensions rather than a highly accurate representation of legal ownership.
About Plat Books
Plat books make use of the Public Land Survey System to represent land ownership patterns on a county-by-county basis. They are a convenient reference for local governments, private realty, surveying companies, and the general public. Commercial plat books for Wisconsin are generally prepared by private map publishing companies in conjunction with county governments. However, recently counties have begun to update the maps themselves.
Plat books are prepared from a variety of source data including U.S. Census TIGER data files, historical local government tax parcel maps, aerial photography, and property descriptions. These records are used to produce a generalized representation of current land ownership patterns, along with planimetric features, such as roads, water bodies, and railroads.
Public and private property depicted on these plats is not considered a full or legally accurate representation of ownership interests or extents, but is a generalized picture, or snapshot-in-time, of the last deed filed on a property at the time the County Register of Deeds’ records were searched. The maps then remain static until they are updated several years later. A “last deed” depiction represents only the last document filed on the property and does not necessarily reveal or resolve full ownership by title or discrepancies in the record.
Complicating this picture, some commercial firms have made it a policy to insert “intentional” errors into the plat books to protect their copyrights, claiming only 85-90% reliability. Thus, while these maps are sufficient for many general purposes, they are not adequate for detailed use requiring high accuracy or current information.
Most commercial plat books are produced as hard copy books and do not necessarily have a true “real world” or integrated mathematical foundation. Today, however, several of these companies are beginning to produce digital versions which – with proper construction, registration, integration, and research of record data – will result in more accurate, current and useful data for many users of land ownership information. Also, another recent trend in plat book publishing has been the use of multiple fill colors in the maps. Color is now being used to differentiate between different types of public lands (national, state, and county forests, public hunting/fishing grounds, state parks, etc.) as well as to indicate private lands enrolled in the state’s Managed Forest Program.