the Standard on Manual Cadastral Maps and Parcel Identifiers and the Standard on Digital Cadastral Maps and Parcel Identifiers.1 These standards are available to IAAO members online and to the public for purchase.

Existing Legacy Parcel Systems

The installed base of existing legacy systems for parcel data production is substantial. Many of these legacy systems are in major metropolitan areas that were the leaders in developing computer-based parcel management systems. A few of these are in heavily populated areas such as Los Angeles that are struggling with the need to migrate their original systems to a modern information infrastructure. Legacy systems have both data quality and political-financial issues. While these older systems may still serve local needs, the data may not adhere to modern standards and may have been compiled from original resources such as paper tax maps that were not as accurate as current resources. One might not expect that these counties, some of which are quite large, would require outside aid to contribute to a national parcel data system, but their substantial existing investment may make them reluctant to modernize. Similarly, they may feel it necessary to charge for their parcel data in order to recoup the costs of their investments. The Southeastern Wisconsin Regional Planning Commission is one example of an area that was a very early adopter and developer of a multipurpose cadastre for the counties in the region. In fact, this was one of the systems cited extensively in earlier National Research Council (NRC) reports as a stellar system. With a relatively large data holding based on the methodology and processes available in the early 1980s (including the North American Datum of 1927 reference system), moving to more modern systems and approaches regionwide was nearly prohibitive. Over time, individual counties in the region, such as Waukesha County, have undertaken migration and modernization, but at much cost and effort. The committee believes that while the need to migrate the GIS environment is a tangible issue in some communities, it is not unique to parcel data systems. Many local government budgets are strained by the constant need to modernize their information hardware and software.

Secure, Reliable Data Storage and Backup

Secure, reliable data storage will be a critical need. Any system that stores and serves data at an individual property level, particularly one that is federally sponsored, will have to meet strict security standards. However, a model that contemplates a national parcel data set of more than 144 million parcels as a federation of dispersed systems, as opposed to a single central repository, faces unique security and reliability challenges. The data must be protected from unauthorized modification and must not be stored in a way that creates the possibility of a single point of failure. For example, data physically stored only at a local level may not be accessible, or may be lost forever, in aftermath of a natural disaster, just when they are needed most. Therefore, backup of data at a physically separate location is important.


Developing a funding model for nationally integrated land parcel data must take into consideration three different elements: (1) the cost to convert all parcel data that has not yet been digitized to digital format; (2) the cost to maintain the parcel data (i.e., to update them when new parcels are formed or information has changed); and (3) the costs to make the data consistent and accessible nationally. Each of these is discussed separately below.


For IAAO standards, see [accessed May 25, 2007].

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement