Wednesday, October 19, 2016

Parcel Data - Authoritative Source and Fitness for Use

The authoritative source for parcel data depends on what type of parcel data.  For tax parcels, the most commonly aggregated and distributed data set, the real estate taxing authority that created them (see who builds parcel data) is the most widely accepted authoritative source. For legal survey boundaries, the land survey record is the authoritative source.  But do we really mean fitness for use?

Authority, authoritative, and authoritativeness always seem to trigger a fairly robust discussion, especially around cadastral data.  A few dictionary-based definitions may be a good starting point.  The following are gathered from various dictionaries and papers on this topic.

Authority and Authoritative - Authoritative is recognized as trustworthy, competent, reliable, and true.  Supported by an authority.  In the context of public agencies it is the legal responsibility provided by a legislative body to conduct business for the public good.

Official - A person invested with the authority of an office.

Authoritative Data – For publicly sourced data these are officially recognized data that can be certified by the public provider, such as a certified tax roll, and is provided by an authoritative source.

Authoritative Data Source – An information technology (IT) term used by system designers to identify a system process that assures the veracity of data sources. All geospatial data providers should follow these IT processes. The data may be original or it may come from one or more external sources all of which are validated for quality and accuracy.

Authoritative Source – An entity that is authorized by a legal authority to develop or manage data for a specific business purpose. The data this entity creates is authoritative data. Authoritative data comes directly from the creator or authoritative source. It is the most current and accurate and has been vetted according to official rules and policy. The data has a known accuracy and lineage and can be verified and certified by data stewards in the authoritative source. In some terminology this is termed the “primary” data source or the “official” data source.

Authorization The result of an act by a legislative or executive body that declares or identifies an agency or organization as an authoritative source or grants the rights to an agency to act, such as an authorization to manage land or collect information.

Data Steward – An organization within an authoritative source that is charged with the collection and maintenance of authoritative data. The term data steward is often confounded with the term authoritative source. A data steward may be a designated point for the assembly and aggregation of data from authoritative sources.

Trusted Source and Trusted Data – A service provider or agency that publishes data from a number of authoritative sources. These publications are often compilations and subsets of the data from more than one authoritative source. It is “trusted” because there is an “official process” for compiling the data from authoritative sources and the limitations, currency, and attributes are known and documented.

In the discussions around a national parcel data set or national parcel data sources, It appears that a discussion and agreement on fitness for use, including some standard or consistent wording or perhaps even categories of fitness for use would come in handy.  We need to answer questions such as “are the values on this parcel from my local assessor and are they official or certified?” or “can I rely on these annexation boundaries as the official boundaries?” or “are these boundaries attached to their definitive source document?” Standard metadata templates include a field for describing intended use or use limitations.  Perhaps it is time to look at providing consistency for these fields.

Many local and state published data sets have a disclaimer that limit the liability of the publisher and provide some general fitness for use such as “not to be used for land transaction legal descriptions”.   A data publisher can never know all possible uses for a data set.  It is likely that some or most data sets will be misused.  Disclaimers try to limit the liability of the data producer if the data are put to some unintended or wholly inappropriate use or relied upon to support an application for which the data was never intended.  This is completely understandable.

As parcel data moves to more open formats and publication, perhaps this is a good time for the community to have some discussions and consensus on expected fitness for use.  This would be more exact and less misunderstood than using terms like authoritative or trusted. 

Friday, August 12, 2016

Parcel Data – Who Aggregates and Distributes It?

Generally state agencies, some regional agencies, and for a fee, a plethora of data vendors. 

The first step is aggregation, which is the process of taking many locally developed parcel data sets and standardizing each to a common format and in some rare cases providing quality control and/or spatially reconciling at the boundaries.  A national standard for parcel attributes exists, ( but as with locally produced data, each state has its own standards to meet its state business needs.  A recent review of state parcel standards found over 20 states had developed state parcel publication standards with many common attributes but no commonality of field names, types, or lengths.  In all states reviewed the state aggregated data did have data definitions and was easier to understand and interpret than individual producer data sets.

The tools used to build aggregated data sets range from brute force to Safe Software’s FME, Esri’s Community Parcel tools, and customized state specific tools.  Most states are either using or moving to web based processing for aggregation. 

Update frequency is typically annually, some are twice a year, and a few are daily or continuous updates. 

Some of the nuances and challenges for data aggregation are described in this article ( 

Distribution has typically been zip file download and a web based viewer.  Files may be a single statewide file but often is individual files for each data provider, such as each town or each county.  A noticeable trend for aggregated and distributed parcel data is the use of feature services. Many national parcel data in federal agencies require a data download to incorporate information into agency systems, but even federal agency applications are increasingly using feature services.

Paul Ramsey presented an intriguing twist to data aggregation and distribution in 2015.  (  Mr. Ramsey discusses relevancy in terms of frequency of use.  If data are not used it is less relevant than data that are used.  Let’s go with the parcel data are important and has many uses, and the parcel data must be relevant.  It must be available to be used and recognized as a useable source to be relevant.

The Moment of Opportunity, as described by Mr. Ramsey, is that small window when data (parcel data) can be provided in a way that developers can easily harvest and embed it in applications that can be seen and used by many on mobile devices.  An interesting implication is that data needs to be distributed in a way that the data can be used and accessed by developers, rather than focusing on end user consumption. 

This is an interesting perspective and important to consider.  As Mr. Ramsey states “it just means that governments need to accept the way that the technology ecosystem is going to want to consume their data, and change their behavior to fit. The first step is to recommit to the idea of data as a public good. If this data (parcel data) is critical infrastructure, as we believe it to be, making it available to all members of civil society, without restriction, is a basic requirement.  … Commit to simplicity in distribution. Follow the lead of NASA and publish raw data, with computer readable manifests, with stable URLs, close to the point of consumption on public cloud infrastructure”

Who distributes parcel data? Generally data aggregators, but we should all keep an eye on distributing our data in ways that will keep it relevant.

Wednesday, July 27, 2016

Parcel Data – Who Shares It?

Some local, some state, some not at all.  Remember when Google first started and the one liner about them was “if you have it, we want it”.  That’s the story for parcel data too.

There are lots and lots of cities and counties that share parcel data with attribution on a regular or periodic basis.  Some update continuously others provide quarterly or annual updates.  A recent survey of parcel producers found there are approximately 6,500 parcel producers (cities, towns and counties) in the US (see Parcel Data - Who Builds it) and of these nearly 70% provided at least viewer or REST Service access to their data and a smaller percentage (around 50%) provided free download and/or open data access. Those that do provide open and/or downloadable access cover almost 80% of the US population and parcel count.

As awesome as digital parcel data are there are certainly understandable reasons why all parcel data is not shared for everyone to have.

The vendor made me do it or proprietary formats - It’s not the mapping formats, it’s the attributes.  Many local governments are tied into real estate tax system (or CAMA) software that has the attributes locked up in either a difficult to extract or expensive to extract data structure.  In a few rare cases the mapping and attribution is managed by outsourcing and the local government doesn’t even own it’s own maps or data.

Once bitten, twice shy - Many local governments have experienced sharing their data with an application or a customer only to be criticized because the supplied parcel data did not meet expectations.   As examples “Why doesn’t this data indicate which homes are owner occupied and which are rented?” “I wanted to see a recent inspection on condition of the structures, where is that information?” I checked this data against my iPhone and the coordinates you have are wrong, I am calling my councilman.” “Where is the mortgage amount in this data set?”  Many of the concerns downstream users have can be explained if the data producer has a chance and if the recipient wants to understand.  Unfortunately, there are too many instances where the criticism gets widely distributed and the explanation (metadata) not so much. 

Show me the money - This has several variants including - We paid good money for this; we are not going to give it away and I need this revenue to fund my office.  These are all, well mostly all, good reasons.  There are many jurisdictions that run short of allocations and automation is not enough to make up the shortfall.  In the Parcel Dial Tone, I mentioned the need for more rural counties and under budgeted offices in particular to charge for data.  Sadly data sales are not likely to be a sustainable revenue stream.  It’s just the way it is.  Consider the path imagery and addresses and elevation and building footprints and so many other data sets have taken.  As technology advances the data becomes more widely and more freely available.  This is not ridicule or undervalue the resource needs of local assessors and parcel mappers.  The needs are real; we just need to find more sustainable and effective funding sources.

It’s mine - Much like parenting sometimes it just comes down to you can’t go to the movies because I say so. Period.  Sometimes this rational is clothed in privacy concerns or “what are you going to do with it?” concerns (see once bitten, twice shy).  Sometimes it’s just that so much personal dedication and commitment has been put into the data, it’s hard to let it go. It’s hard to not take ownership of it.  I have always thought that parcel data is personal.  It’s the most personal of all locally maintained data sets.  The data producer’s fingerprints are all over this data set and having a sense of ownership is certainly understandable.

Who shares parcel data? The most recent detectable trend is more and more parcel producers are sharing, especially cities, lots of cities.  

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.