My first foray with ArcGIS Online

Now that the dust has settled and AGOL is almost old hat, it must be time to give a roll.  I started with a relatively simple idea for a web map and thought this would be a test and I know a lot of you are making the same start, because I see lots of maps on AGOL with names like test, test1, map1, first day, try this, etc.  

A few disclaimers, I am reasonably well versed in ArcGIS, working knowledge of spreadsheets but I don’t live there, extensive database knowledge, moderately knowledgeable about web map pages, although Karen and Jason do my heavy lifting, abandoned my inhouse server about 6 months ago, and moderately skeptical about service credits. Lindsay and Ken provided tips and tricks and debugging for some of my more stupid mistakes.  After about 16 hours, not all of it productive time, here are a few things I learned that might save you some time.

False Step 1 - Do not take your great looking desk top mxd with all of the symbology, layer files, and base maps that you use for your local analysis and editing and just push it to AGOL.  The idea that you can “simply” publish any mxd to an AGOL web page is sort of true, but this results in a lot of lost time for a really bad looking, under performing web map that you really didn’t want to use as a web product anyway.

Good Step 1 - Take the time to really get into your AGOL account.  Get your profile set up, establish the groups you want, add the icons, think about the key words, you are going to be using them a lot, so get a list you like.  Thinking time and image and icon prep is all worth it.  It might take you a few hours to get a good base established but it is time well spent.  Think about the pattern and style for user logins, they will be using them more than you think and should follow some pattern you can quickly recall.

Good Step 2 - Design an mxd for a web map, not your desktop but a web map, what do you want to show or not show what will be the information about that layer that you will want to see.  This took a bit to think through and had several false starts but I didn’t want to start with a template, for this experience I wanted to see what it looked like starting from scratch, or nearly so.

False Step 2 - Yep, the projection thing, seems like 100 years ago we were arm wrestling projections and coordinate systems and datums.  So now we are at the Web Mercator Auxiliary Sphere 2, or whatever, and yes you do use the project command or project tool, seems like the good ole days.  Of course you could “simply” geocode your data, but again I wanted to take my data and put it on AGOL. 

False Step 3 - Project your data BEFORE you build the mxd.  If you build an mxd, then project data, and relink your mxd to the newly projected data, some how the attributes never get to the AGOL site.  Sequence is important here, sort of like putting the targets down before the airplane flies over.

Good Step 3 - Fix all of the errors reported in the Analyze step.  Sure some of them are listed as minor or low level or insignificant, don’t believe it, they are checked for a reason and they will bite you at some point, just fix them.

Good Step 4 - Save at every opportunity.  You cannot save frequently enough.  Configure the pop up, save the pop up, save the map.  Change the transparency, save the map. Change the edit properties, save the map. And save the pop up information somewhere, even though you cannot actually cut and paste into the pop up configuration window, at least you will know what you did. And save the map again just to be sure.

False Step 4 - Don’t worry about how the html or web links are going to look, you can’t really change them anyway and the AGOL does a reasonable job of adding the “more info” link in the pop up, although it does not recognize ftp sites as web links and you cannot insert a field name into the custom configured link. 

Good Step 5 - Overwrite the service when you update the data.  Yes, you can do some editing to the data on the AGOL site, but then your desktop data is out of date. Just update it on the desktop and republish. The “overwrite service” option works pretty well, just remember that after you do overwrite, you have to re-share the feature service; I spent too much time “debugging” that.

In the end, I think the AGOL is a good deal.  I consumed 3 service credits messing around with multiple uploads and false starts, but learned a lot.  Check it out http://bit.ly/141df5V.

I sense that one of the primary audiences for the AGOL will be the non-traditional GIS types who might have used Google fusion or some other quick web map tool, so my next experiments will be to see how simple the csv and Excel format are to use and to use the story map templates to build a web page.  I am curious how this experience will fit with my Google publishing experience.  

Parcel Identifiers - Standards and Practice

Parcel Identifiers

A Review of Standards and Practice

There are many systems and specifications for parcel identifiers.  Most of these are associated with real estate tax systems but there are also parcel ownership identifiers, real estate improvement identifiers land transaction identifiers, generally on publicly managed lands.  This document reviews some of the recent standards and some best practices for parcel identifiers.

Standards

The International Association of Assessing Officers (IAAO) has an established standard for cadastral mapping and parcel identification systems. This standard was revised in January 2012.

This standard provides recommendations on the development and maintenance of digital cadastral assessment maps, parcel data layers in a geographic information system, and parcel identifiers.[1]

IAAO is one of the standard making bodies for property assessment and valuation. The IAAO recognized the importance of parcel numbers across municipalities and developed a set of core recommendations for creating these PINs.

·       Compliance with Standards - The PIN should conform to defined standards including national, state and local standards.

·       Uniqueness – The most important aspect of the PIN is that it be unique.

·       Permanence – PINs should be permanent and only be changed in extreme circumstance.

·       Simplicity and Ease of Use – PINs should be as short as possible, uncomplicated, and easily understood.

·       Ease of Maintenance – The PIN should be easily maintained and accommodate changes such as a split or merge operation.

·       Flexibility – The PIN should also be flexible to accommodate not just land but multi-family dwellings, sub surface rights, leases, etc.

IAAO defines a parcel, a feature that is assigned a PIN, as a single, discrete piece of land having defined physical boundaries and capable of being separately conveyed.

In another national standards effort, Mortgage Industry Standards Maintenance Organization (MISMO)[2] has formed a working group to develop a national parcel identification system. MISMO was formerly a part of the Mortgage Electronic Registration Systems (MERS) and has recently been brought under the Mortgage Bankers Association (MBA).  The mortgage industry currently uses a combination of postal addresses, legal descriptions, assessor parcel numbers and geospatial coordinates to track homes. The MISMO Development Working Group (DWG) will focus on the development of universally accepted system parcel identification for the future mortgage market.

There is no universal standard for identifying a property, resulting in greater risk for mistakes and fraud. This proposed DWG seeks to bring together industry representatives to talk about current challenges, and possible enhancements for improving data standards in the realm of property location definition, verification and best practices. [3]

Another standard’s body is the Property Records Industry Association (PRIA), which was founded on the concept that government and business can work together to address issues of common concern in the world of property transactions.[4]  PRIA has established a GIS working group that has the following charge.

A recent estimate shows approximately 70% of all local governments have implemented some form of GIS.  Yet in many cases GIS is not integrated with the recording office. The PRIA GIS Workgroup has been chartered to establish standards, procedures and best practices for data exchange between GIS systems and land records systems. This will allow the exchange of information while taking into account performance, security, and revenue implications.

This group has not completed standards development but is working toward a national parcel identification system that will allow linkage between GIS features and source documents.

The FGDC Cadastral Data Content Standard and the core parcel publication guidelines derived from that standard also calls for a nationally unique parcel identifier.  In the case of the FGDC standard the national standard leaves the local parcel identifier in tact and appends the jurisdictions Federal Information Processing System (FIPS) code to the front of the local identifier.  The FIPS code assigned is determined from the supplying data steward.

The Open Standards Consortium for Real Estate (OSCRE) statement of purpose is “effective open standards are crucial for sharing information across boundaries and for systems that more easily interconnect.  Standards play a key role in innovation by giving businesses more choice in the software they use by reducing vendor lock-in and reduce the cost of IT by enabling a more competitive and diverse market.”[5]  OSCRE is a more international standards body than the others. In 2005 DoD adopted an agency wide real property unique identifier (RPUID) that was endorsed by OSCRE as a commercial best practice.[6]  The DoD’s RPUID is assigned to structures rather than land.  Every DoD building and structure is assigned a single number for its entire lifecycle. RPUIDs are tracked centrally in a registry and any authorized system in DoD can obtain information about a building by using the RPUID and web services to check the registry.

Each of the standards bodies has a slightly different need for a national identifier.  The activities and lessons learned from these standards organizations provide guidance on developing a parcel identification system.  One of the most important lessons seen throughout all of these standards organizations is to complete and unambiguous definitions of the feature being identified.    MISMO is focused on features that are identified in mortgage and loan documents, IAAO is focused on features that are assessed or taxed, PRIA is focused on connecting land descriptions to conveyance and other recorded documents, FGDC Cadastral Subcommittee is focused on maintaining the data steward’s identification number while allowing for national uniqueness, and OSCRE is focused on identifiers in the system architecture and business processes.  DoD’s implementation focused on buildings and structures.

Public Lands

None of the existing standards reviewed specifically address how public lands (non-taxable from a local government perspective) are assigned a parcel identifier and what defines the extent of the publically managed parcel.  In some areas of the public domain lands there are vast areas that have neither a survey nor a case transaction.  In these cases what is the best method for assigning a unique identifier to the land area that will define and relate to the land in a meaningful way and also be maintainable over time. Should every permit or transaction generate a new parcel identifier or should the parcel identifier be based only on the underlying land description and land survey? 

Two federal land management agencies, the Forest Service (FS) and the Fish and Wildland Service (FWS), currently use parcel identifiers.  In the FS system a master geodatabase is stored in a centralized location in Kansas City and is accessed through Citrix.  The updates are in real time using Oracle Spatial and the geodatabase is not versioned.  FS uses FME scripting to translate the production data into the publication data sets.  The enterprise data warehouse supports generating publication data and web-based services to support the decision support needs of the FS. The publication database is designed to support regular reporting needs such as the Land Area Report (LAR). The original FS withdrawal is assigned a parcel number and subsequent acquisitions or withdrawal actions are added with an assigned separate parcel identifier.  FWS does not maintain a BLM Case Serial number for acquisitions or withdrawals but does have a nationally internal unique parcel number for all parcels.  The original defined acquisition authorization area has a parcel identifier, as do all subsequent acquisitions with each conveyance or land ownership change assigned a new parcel identifier.  There was a large reconciliation project that worked through the FWS Lands database and the GIS to finalize and establish the unique parcel identifier across all systems.

In the Montana Cadastral System the publicly managed lands did not have a parcel identifier at the start because these lands were exempt from property tax systems.  But as the CAMA and GIS grew the need for an identifier for public lands (state, federal and county managed lands) became more apparent.  Attributes about the management agency and any actions on the lands had to be linked to the spatial feature in the GIS.  The publicly managed lands, including federally managed lands, are assigned a parcel identifier that is in part a geocode that identifies the county, the PLSS Township, section and if applicable, quarter section.  No parcel is larger than a section.  Federal lands smaller than a section are identified to either the quarter section and then further divisions according to the state DOR system for tagging areas smaller than a quarter section.

This system has worked well in Montana and although it is not synchronized with BLM records, as parcels are exchanged or apparent parcel configurations are changed, parcel identifiers are updated.  Montana recognized that the BLM often has a more granular definition of their land based on case actions.  Although desired, the state does not have a link to records in LR2000 that would facilitate a more complete representation of land transactions on federally managed lands in the Montana Cadastral System.

State Systems

Many state departments of revenue or taxation have some guidance on tax parcel identification; Florida, North Carolina, and Utah are three examples.  The state guidelines may or may not be enforced and there is significant variation in local governments even with state guidelines.  Utah’s state parcel identification guidelines provide three system or methods for parcel identification and summarizes these three commonly used systems.[7]

Proper identification of properties is essential to accurate valuation. A parcel identification system provides a method for referencing land parcels or data associated with parcels, using a number or code instead of a complete legal description.

It is important that the parcel numbering system allow the user to locate the parcel by means of the unique number. There are three kinds of numbering systems, which are suitable for this purpose.

Map-base

In a map-base system, the first number sequence is assigned to a map, the second number sequence to a block or other organized map division, and the last to the individual parcel. An alternative map-base system is called a book-page system. The first number sequence is assigned to a book of maps, the second number sequence to a map page within the book, and the third to a parcel on the map.

Government Survey

The government survey takes for a base the existing land survey system of townships and ranges. The numbering sequences correlate with sections, quarter sections and other such subdivisions as necessary until the last number sequence, which refers to the individual parcel.

Geographic Coordinate Code (Geocode)

The geocode system is typically used on a computerized (GIS) system where the approximate center (paracentroid) of each parcel is identified. The parcel is numbered based on its x (east-west) location and y (north-south) location. Although the geocode system is accurate and quick, the parcel numbers do not tie directly to any given map or block. When a GIS mapping system is utilized, coordination with the AGRC is required to facilitate uniformity, data transfer, numbering schemes and formats used in parcel identification.

Local Systems

There are almost as many variations in local parcel identification systems as there are local systems.  Although the emergence of national CAMA vendors such as Thomson Reuters, Tyler Technologies, and Orion have reduced the number of local variations as these system each enforce consistent parcel identification requirements. It is not uncommon for a county to maintain several parcel identifiers with municipalities, the assessor, the treasurer and the planning agency each assigning a separate identifier. 

From a national perspective organizations that consume parcel data from many local jurisdictions especially across state lines are often confused about the formats and content of the parcel identifier.  While it is often possible to make each county’s parcel identifier unique by appending a local jurisdiction code to the front of the number, the structure of the parcel identifier, the content, special characters such as dashes or periods, and inconsistent usage such as the reuse of parcel numbers creates uncertainty when other data is connected to the local parcel data sets.  This typically happens with value added commercial data providers but can also occur in many other situations when the parcel data is used as base data for an application or to support a business need.

Conclusion

The basis for the identification number, whether it is computer generated or based on the parcel location or the parcel characteristics, was not found to be as critical for success, as the following.

(1)  The parcel being identified is well defined, recognized, and unambiguous.  For example are parcel identifiers attached to ownership parcels or to tax parcels?

(2)  The identification system, whether a number or intelligent key, must be unique across the entire system, never duplicated, and be easily generated.   

(3)  The parcel identification remains unchanged throughout the parcel’s life cycle, such as if the geometry of the parcel does not change than the parcel number should not change, and

(4)  The parcel identifier must be able to be used to link to related records and documents.

---

[1] http://www.iaao.org/uploads/Standard_Digital_Cadastral_Mapping.pdf last accessed 10-2-2012.

[2] MISMO®, the leading technology standards development body for the residential and commercial real estate finance industries, is a wholly owned subsidiary of the Mortgage Bankers Association. From http://www.mismo.org last accessed 10-2-2012.

[3] http://www.mismo.org/files/PressReleases/NewDWGPressRelease9_14_2012.pdf, last accessed 10-2-2012.

[4] http://www.pria.us/i4a/pages/index.cfm?pageid=1, last accessed 10-2-2012.

[5] http://www.oscre.org, last accessed 10-2-2012.

[6] http://www.oscre.org/node/414, last accessed 10-2-2012.

[7] http://propertytax.utah.gov/library/pdf/standards/standard08.pdf, last accessed 10-2-2012

Parcel Data: Is it a Public Good?

In December 2010 Planet Money Team broadcast an article on “What Should Government Pay For? Autopsies and Lighthouses”

http://www.npr.org/blogs/money/2010/12/10/131784161/what-should-the-government-pay-for-autopsies-lighthouses

A few interesting quotes from this article

“Lawmakers have spent a lot of time lately debating what to do about the country's growing deficit. In doing so, they're wrestling with the question that goes back to the beginning of the Republic: What should the government spend its money on?

A public good is something that we all need, that will make our lives better - but that the market will not and cannot provide.”

In the case for lighthouses the point was that initially there were some privately built lighthouses but in 1789, the government set up what would become the U.S. Lighthouse Service, which built lighthouses in places that were hard to get to and expensive to build.

In the case of autopsies the Journal of the American Medical Association has been arguing for 15 years, at least, that there's a public health problem because we're not doing enough autopsies. The autopsy rate has plummeted from 40-some percent down single digits. If we add more autopsies, we'd know more about how people die. So collectively, we all want them. And yet, no individual really has an incentive to pay for one. They don't see the benefit.

If we look at parcel data with some of these economic tenets we find

• Similar to lighthouses the private sector is very interested in parcel data at least in urban America, but not so much in the more rural or even poorer areas of the country. Yes there are some firms and maybe even an increasing number of firms offering parcel data, but maybe not evenly across the country and certainly not in the public domain.
• Similar to autopsies the individual parcel producer, typically the county, does not see the benefit in offering their individual data sets, there is no real incentive. There are benefits to reducing the time to process requests and to comply with open records laws, but no consist nationwide policy or direct benefit has been established.

Yet we see time and again multiple federal and state agencies and private organizations that have a need for parcel level information even if no one application actually needs all of the nation's parcels at one time, there are many needs for parcel information that cross county boundaries in sporadic geography across the nation. There is a need for nationwide parcel, just not all in one data set at once.

So is parcel data one of those public goods? Even in these tight economic times maybe we should be looking at pooled funding among the federal agencies that need the data, the local governments that produce the data, the states that could publish compilations of the data and the private sector that uses it as a base for enhanced services to fill a public need. Surely we have the technology to make this happen, but is there a sufficient institutional will and the case for the public good to make it happen?

Cadastral/Parcel Mapping Quality Components

We are often asked “how good is that parcel mapping?” or “how accurate does my parcel mapping need to be?” Unlike data sets that are built from a single source, such as aerial imagery or topographic maps or lidar, the answer to the questions of how good or how accurate for parcel mapping is a case by case, parcel by parcel response. Certainly the results of an analysis could be rolled up to a statement about the overall data set but the quality of parcel data is much more than just spatial accuracy. What are the quality components for parcel or cadastral mapping?

Currency – How current is the parcel map?

The currency can be stated as simply as this parcel map includes all land transactions as of last Friday, or within one month or as of yesterday. The currency statement for the mapping might be different than the currency of the associated attributes or attributes that the map may be tied to. For example the assessment value information might be from last year. A parcel split might be current as of yesterday but the assessment values for the new parcels might be from the prior year until the year-end assessment information is brought current. The mapping currency should be stated separately from the related attributes.

Completeness – How complete is the parcel map?

At first glance most organizations might reply 100% complete, we map everything. But consider if the parcel map includes federally managed lands, are these mapped and indicated as federally managed land and does it reconcile with the federal agencies mapping of the same parcel? Are state managed lands included? Are right of ways included? Is this parcel mapping taxable lands? If it is taxable lands are all taxable lands on the roll represented on the map? Typically an ongoing parcel program will have 100% coverage for the parcels they are mapping, but it is always worth an extra look to be sure.

Lineage – Does every parcel polygon have a link to its source document?

An important part of the parcel mapping process is recognizing that it is a representation of the descriptions and content of the legal document from which it was generated. These documents can be survey plats, deeds, right of way plats or any number of types of conveyance documents. Providing a link to the source document that was used to define the geometry is an important and essential component of the parcel mapping. Note that this is the link to the document that defined the geometry and may not be the same as the document that contains information on the current owner.

Relative Positioning or Closure – Does every polygon have an indicator of the relative accuracy of the legal description?

For organizations that run coordinate geometry on their parcel it is possible to get a record of the linear error of closure (LEC) of the legal description, however not every organization uses coordinate geometry for parcel mapping and some legal descriptions are just not suited for this type of analysis. For example a parcel legal description may call out a river centerline or a physical feature such as a tree or road and the measurements to execute a linear error of closure analysis are not easily derived. To solve this it may be possible to develop a simple coding scheme that indicates the general quality of the associated legal description for the parcel polygon. For example the relative positioning codes could be something like the following.

1 – parcel closed, LEC at least 1 part in 1,000.

2 – parcel closed but the LEC was less than 1 part in 1,000 or one line of the parcel was a physical feature call that matched the imagery closely.

3 – parcel is drawn entirely from reference to imagery and physical references and these calls match the imagery.

4 – parcel metes and bounds description did not close and had to be best fit with surrounding parcel or imagery evidence.

5 – parcel closure or relative accuracy could not be ascertained or assigned.

6 – no attempt was made to determine the parcel relative accuracy.

These are just an example of some the things to consider in a relative accuracy coding. Another alternative might be to assign the LEC as the relative accuracy and indicate if no LEC was determined.

Absolute Positioning – How well odes the parcel legal description match control point location of the boundary?

This is the most traditional indication of “accuracy”. This is an indication of how well the parcel fits with other parcels and how well it ties to control measurements. For example if the corners of a subdivision have been located with global positioning system (GPS) how close is the corner location on the parcel map to that GPS location? Similarly if an organization has jurisdiction-wide orthoimagery, how close are the physical calls in the legal descriptions to the visual evidence on the imagery? F a parcel description runs to the middle of the road does the parcel mapping show the parcel line on the middle of the road, assuming the road on the imagery is the same road called for the legal description. Beware of the difference between the center of the right of way and the center of the road. These are often different. Even with the nuances of legal descriptions and visible evidence it is often possible to use the imagery to get a sense of the absolute positioning of the parcel maps.

Attributes Present – Are all of the attributes for the parcel map included?

This is a check of the parcel map database to assure that all of the parcel polygons have the attributes they are supposed to have. If the parcel has a tax identifier, is it entered into the parcel map database and is it correct? If the parcel map database uses annotation, are the annotation fields complete and correct? This evaluation would also apply to systems that use line types or any other codes for cartographic display or parcel classification.

The following two components are indications of the overall parcel mapping program in an organization. These components might be termed best practice as opposed to quality components, but these two components contribute to the overall quality of the parcel mapping.

Archived Data – Does the parcel mapping program include tracking historically mapped parcels?

Archiving data might be as simple as taking an annual snap shot of the parcel mapping database and archiving with the backup data. It could also be snap shots of the data periodically such as monthly or quarterly. In a transaction based parcel mapping system each parcel change will result in archiving the changed parcel to an historical parcel file or something similar so the parcel map can be used to “roll back” through time and visual observe changes. Parcel data that is archived in this manner typically keep the parcel number and linkages to source documents with the historical geometry.

Maintenance Process – Is there a documented and sustainable maintenance process in place?

Because parcel and cadastral data are so dynamic, potentially changing on a daily basis, it is important to have a defined and sustained maintenance process. A parcel map may be perfect at the moment it is delivered from conversion process, but it will soon be out of date if there is not a sustainable maintenance process. This means the updates and maintenance have to be consistently and on a regular basis. Even if that basis is once a year, it is a known maintenance cycle.

The reason organizations invest in parcel mapping is to use the resulting with related data such as the tax roll or deed recording or permitting or zoning or a plethora of other applications. The last three components of parcel mapping data quality categorize the data distribution or data publication. This is separate from the evaluation of the production data.

Publishing Schedule - Is the parcel map published on a regular schedule?

Do the customers for the parcel data know when to expect parcel mapping updates? Are updates provided or notification of updates made available to those who depend on the data. Notification might be that the most current information is pushed to a data service and when users add the data to their canvas the updates are reflected on their project without the need for additional notification.

Metadata – Does your published parcel data have essential metadata?

Metadata does not have to be onerous. If an organization focuses on establishing essential metadata for published data, then the metadata should be relatively stable and can be published with the data set as an XML file or as an html file or embedded in the distributed or published data set. With limited resources there is less demand for metadata for production data, data that is internal to the organization than there is for published data that will be likely be consumed by people who have little or no local knowledge. The FGDC Cadastral Subcommittee has developed a limited set of essential metadata and tools for creating the published version of this data, that can be found at this link http://www.nationalcad.org/showdocs.asp?docid=1153&navsrc=Standards&navsrc2=

Attributes Standardized – Are the attributes in the published data translated to standard naming conventions and content?

The FGDC Cadastral Subcommittee has developed a publication standard for core parcel data. This is a minimum set of information that meets a large audience of data requests. Some organization have added to this core level information but the goal is to encourage all published parcel data to be in or have a version of the published data that matches this standard. Added attributes are a bonus. The publication guideline can be found at this link.

http://www.nationalcad.org/showdocs.asp?docid=1149&navsrc=Standards&navsrc2=

So how good is your parcel map? Applying some or all of these quality measures and then developing an evaluation rating might be one way to answer that question. It should also be a way to measure the increasing quality of the parcel map as the maintenance progresses.

Authoritative Cadastral Data

Unlike other spatial data (hydrography, topography, orthoimagery, etc), cadastral data defines rights and interests in land. Cadastral data are also unique because it is created and maintained by over 4,000 separate entities across the country.

The vision for the National Spatial Data Infrastructure (NSDI) and the National Cadastre within the NSDI is to have a single source of authoritative cadastral data that is controlled and managed by designated data stewards. Access to this data is facilitated by compiling and integrating the data into trusted data sources at state or regional levels. This will reduce duplication of effort and assure that the best available information is used in decision-making.

Cadastral data includes assessment records that support the real estate property tax system, recorded land documents such as deeds and mortgages, indices and summaries of this data such as a grantor-grantee and tract indexes, and survey information captured in plats and surveys.

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.

Trusted data describes data sets that are published by someone other than the authoritative source and is often the compilation of multiple sources of authoritative data. It is “trusted” because there is an “official process” for compiling the data from authoritative sources and the limitations, currency and attributes are known. The data are often formatted into a standardized form and linkages to the originating source are provided with the data. This trusted source is recognized by the authoritative source as an “official” publisher of this subset. Typically a trusted source is established to integrate data from multiple jurisdictions and to compile it into a standard format. This trusted data is adequate, convenient and cost effective for users who need a regional view and have to deal with multiple sources of data, but there is an understanding of the necessity when final decisions are being made, particularly about rights and interests of specific properties, that the user must go to an authoritative source and acquire authoritative data directly to ensure that they have the most current an accurate data.

Data stewards have the responsibility to organize, collect, maintain and provide data. Data stewards are those closest to the data creation, they have recognized expertise in the field and follow professional standards.

When there is not a single source for data, such as nationwide assessment data which has over 4,000 local government sources, and the effort to acquire authoritative data from individual authoritative sources is impractical, then it is reasonable to acquire trusted data from a trusted source.

All cadastral data collections that do not come from authoritative or trusted sources are “unofficial” or “shadow” copies whose value degrades over time relative to the rate of updates to the authoritative data. Unofficial data is often duplicative and creates redundancy by re-publishing data that are already available from a trusted source. Unofficial sources create confusion among the general consuming public by providing un-maintained duplicative data and “unofficial” parcel-like data sets that can unexpectedly harm or damage property rights with inaccurate out of date information.

Recognizing the importance of authoritative sources for authoritative cadastral data that may be provided through a trusted source will be essential to protect individual land rights, to support local governments and other parcel producers in their authorized role of data stewards and to ensure that the user community has the best available and most current cadastral information.

The FGDC Subcommittee for Cadastral Data, following the directives in OMB Circular A-16, has developed a series of documents over the past ten years that describe the concepts and polices related to the creation, use and publication of cadastral data. There is more information on authoritative and trusted sources for cadastral and data stewards for various components of cadastral data at the FGDC Subcommittee’s publication site (http://www.nationalcad.org)