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.

1 comment:

  1. This is an interesting internet article on realtors use of parcel data holdings. The Multiple Listing Service (MLS) and Zillow are two of the parcel holdings discussed.