Friday, July 15, 2016

Parcel Data – Who Builds It?

Local governments mostly.  And often the most local government meaning the town, city, township, or county.  In some cases, the state prepares parcel data on behalf of the local government. Parcels and addresses are the most local government data.  Constructed closest to the citizen. 
In addition to the obvious tax assessment, real estate billing, and real estate tax management, parcels, generally tax parcels, are used many local functions like permitting, land use planning, zoning management, land banks, public lands management, and many many more. 

Parcel data aggregation combines data from multiple data maintainers into single standardized data sets.  Most parcel data aggregation occurs at state or regional government levels.  There are also many cases where counties (and their equivalents) are aggregating digital parcel data from cities and towns).  County level aggregation often requires maintaining and reconciling common boundaries for a seamless representation.  Regional and state level aggregation is less likely to reconcile common boundaries. There is an increasing trend for states to build standardized aggregated parcel data sets to support statewide value equalization, state disaster response and recovery functions, broadband access management, and many other cross jurisdictional business needs.

An inventory map of the local governments that have digital parcel maps can be found at this link (  This is a voluntarily maintained inventory and is not positively complete and accurate but it is a good indication that about 90 % of the 150 million parcels in the US have been mapped into a GIS or automated mapping software of some type.

That is just the mapping.  Real estate valuation and tax attributes are 100% automated at some level.  Yes, there are still jurisdictions that have hand written, hardcopy individual property assessment cards, but a recent national inventory did not find any jurisdiction that hand generated real estate tax bills.  Every jurisdiction was covered by or represented in a Computer Aided Mass Appraisal (CAMA) or similarly functioning system even if the most local officials did not have the software.
The attribute data are by no means standard.  Similar attributes are named and structured differently, data are collected or entered at different times, the basis of the attributes values, and extent of attribution vary greatly.  Adding to the variation, there are well over 75 software vendors each with local installation customizations.

Local governments build parcel data and each one builds it and maintains it uniquely. 

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