Editor’s Note: The following is summary of CoreLogic’s nationwide parcel database that was provided by CoreLogic, followed by a short Q & A from Eric Gakstatter and the end of the article.
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When the Trust for Public Land (TPL)began organizing its extensive conservation research and project information, its executives planned several database initiatives to showcase the volume of land that has been conserved for public use to date. Already innovators in funding conservation projects and city park creation, the TPL team set a goal of using GIS technology to make it easy for government agencies and other partner organizations to find the information they need to generate public funding for land conservation. The challenge: Organizing decades’ worth of comprehensive research and historical project information to accurately depict the true volume of U.S. land conservation.
The initial project, TPL’s Protected Places Inventory (PPI), involved modernizing a database that included over 4,500 land projects spanning more than 40 years of conservation work. TPL knew the database needed nationwide parcel data to produce reports that would give urban residents, city officials and elected representatives more detailed information—such as the percentage of residents in the nation’s 40 largest cities who live within a half-mile of a park.
The National Conservation Easement Database (NCED) resulted from collaboration with four other leading conservation organizations to provide a comprehensive view of an estimated 40 million acres of privately owned conservation easement lands throughout the country. When TPL and its partners—Ducks Unlimited, Defenders of Wildlife, NatureServe and the Conservation Biology Institute—began work on what would become the NCED, the team discovered that many land trusts and entities that manage easements did not have those easements mapped at the parcel level. By mapping conservation easements at the parcel level, the easement database offers government agencies, land trusts and conservation professionals a more accurate assessment of an easement’s size and location.
Another project, the Conservation Almanac, which was developed around the same time as the Protected Places Inventory, presented a similar opportunity to enhance historical records with parcel-level data. Designed to track land area conservation activity across the U.S., the Conservation Almanac helps key stakeholders understand the context of land conservation and funding from both the public and private sectors. This database helps answer common questions, such as how much land has been protected per state, which state and federal agencies have protected land, and what the cost to protect that land was.
“When looking to add to our databases, we soon discovered that in some areas, parcel data either didn’t exist or was so expensive through the local government that it prohibited our organization from economically acquiring it,” said Breece Robertson, TPL’s national conservation vision and GIS director. “Additionally, the data we did finally acquire was often outdated or incomplete.”
With that in mind, TPL began a search to find a cost-effective single source for nationwide parcel data. The organization found a solution through CoreLogic ParcelPoint, the largest standardized nationwide property database, which contains data for 134 million parcels, covering 2,391 counties and representing 93.6 percent of the U.S. population.
Source: CoreLogic
Source: CoreLogic
“With the help of CoreLogic, the organization’s budget for adding parcel data was significantly reduced, and the PPI project took a single year to complete instead of the estimated five years ,” said Robertson. “Plus, with more than 4,500 completed projects in the Protected Places Inventory database, it’s not only easier to keep the parcel boundary information current, but entering new projects now only takes 15 minutes instead of the previous three hours.”
Q & A on ParcelPoint
Gakstatter: What was the range of costs you were quoted from local governments for parcel data?
CoreLogic: It ranges from $60 for them to get the data onto a disk to mail to us, to upwards of $3-4k. One county in California quoted us $10k for their parcel data, another used to charge $1 million for their parcel data but they’ve since been forced to offer it for a nominal “packaging” fee.
Gakstatter: Are you going to/Did you enhance the parcel data you acquired? With what data and how?
CoreLogic: In some cases, we ran parcel prioritization analyses on the parcel data using many other datasets to show where priorities stack up on the landscape, such as size of parcel, adjacency to protected lands, adjacency to wildlife habitat areas, parcels that flood during storm events, etc. The parcels get tagged with a score or metric depending on how important it is for conservation based on a variety of inputs.
Gakstatter: Which horizontal datum do you use for your nationwide database? What is the estimated horizontal accuracy of the database?
CoreLogic: For all of our projects, we work locally so we always have to clip out the parcel data we need for an area and re-project that using either the local UTM or state plane projections.
Added 4/12/13 from CoreLogic: Spatial accuracy can be highly variable depending on the source of the data and the methods under which the data are created. CoreLogic employs statistically valid testing methodologies based on guidelines developed by the Federal Geographic Data Committee (FGDC) to provide quantitative and statistically valid accuracy statistics for the vast majority of counties within ParcelPoint. During the most recent compilation, the overall ParcelPoint dataset tested approximately five meters (15 feet) horizontal accuracy with a 95 percent confidence interval.
Gakstatter: Can you expand on the three programs and the process you went through to compile data before going “modern” with ParcelPoint?
CoreLogic: For all three programs, it was the same. We’d have to do a Google search to see if parcel data was readily available online. If not, we got a contact phone number for the local assessor’s office and contacted them. At that point, we found out what type of license agreement we would need to sign, or if there was a fee for the data. At that point, we would have to figure out if the license agreement was too stringent or if the cost of purchasing the data was prohibitive. We involved our legal staff to review the license agreements and provide suggested changes or write up addendum stating our use of the data for the county or city to consider. That process was expensive (in staff time) and took a long time with all of the back and forth. Finally, when we received the parcel data, if we were working on a project that spanned many counties or cities, we’d have to using GIS tools to project the data and stitch it together – running into issues like datasets not matching up or overlapping parcels, etc. With ParcelPoint, we just go to the database, clip out what we need and we are off and running. What used to take weeks or months to just acquire the parcel data from various entities now takes 15 minutes.
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