As illustrated throughout this report, parcel data is employed in a very wide range of public, private, and civic uses. However, almost every person interviewed expressed a desire for better quality data. Most users spend considerable resources obtaining, improving, and standardizing parcel data before they are able to use it for their own needs. Much of this cost is associated with an organization’s need to supplement, verify, correct, or integrate data collected by others. Even when the data they begin with is of high quality, however, it may not be sufficiently detailed or readily comparable to other sources, or derived from systems that are technically compatible. All of these problems make parcel data more difficult and more expensive to use.

One of the most obvious issues for data users is the inverted relationship between geographic coverage and the timeliness, detail, and completeness of parcel data. At the point of basic data collection, generally conducted by municipal assessors, parcel data is most up-to-date and contains the most detail regarding a variety of attributes. Most municipalities report assessment data to the county and state levels only once a year but some municipalities do not report all of their parcel inventory and improvement data.

At the county level a new kind of information is maintained in the form of tax maps, but the county tax maps and assessment rolls are not as detailed as the information in the municipal assessors offices. When ORPS supplies data files to the statewide GIS Clearinghouse, the files contain even less detail, generally comprising about 25 descriptive attributes and usually the parcel centroid (i.e., the location of the approximate geographic center of a parcel). Thus a user seeking statewide information from a single source has access to the smallest amount of information, while a user whose purpose is limited to single town can make use of the greatest amount of information. Figure 2 below illustrates this paradox:

Figure 2. The paradox of data coverage and detail

As a consequence of this paradox, any use which requires regional or statewide information also requires the user to make many separate requests from different data suppliers. Usually requests go to counties where the tax maps and associated attribute data offer relatively good basic coverage for most applications. However, this process is time-consuming, costly, and unpredictable because counties do not follow uniform procedures or policies for dealing with data requesters. These problems and expenses add to the cost of many projects and can sometimes cause users to abandon their projects.

In addition, most uses require data from other sources or require data that is more detailed than that collected in the process of real property tax functions. For example, most engineering uses require survey quality data, which tax maps do not provide. Such users did not expect that county or municipal data should meet this standard, but they believed that their own data investments should be devoted to expanding or supplementing this basic data, not to acquiring it (or correcting it) in the first place.

Interviewees also mentioned incompatible technologies as a barrier to more effective data use. For example, not all parcel maps use the same mapping projection, which is a mathematical model for converting locations on the earth's surface in a way that allows flat maps to depict three dimensional features. Although some technologies convert files originating from different mapping projections easily, there are still others that do not preserve the integrity of shape, the accuracy of area, distance, or direction.