Assigning Parcel IDs
Hogan County is used to illustrate assigning parcel identification. Parcel assignment and use considerations are described using typical examples.
Hogan County has a parcel map with parcel identifiers that are unique across the county. The county has mapped tax parcels but has also accounted for all the area in the county. That is, while parcels that are subject to property tax have been the focus of the mapping, tax-exempt lands, such as roads and federal lands, have also been mapped and given a number. In this example, all rights of way have been tagged as Tax Parcel ID 98 and all Federal Lands have been tagged as Tax Parcel ID 99. Other departments in Hogan County also use the Parcel IDs for related information such as septic and building permits. In Hogan County the Parcel ID is added to the septic and building permit applications and provides a way for other departments to determine owner and value information about the parcel where the septic and building permit are located.
In Hogan County, Figure 1 above, the parcel identification for the parcel data would be linked to other Hogan County information through the assigned tax number, including the tax roll, well and septic permits, and other information. The parcel map includes parcel outlines and examples of tables with related data that is tied to Parcel IDs. In Example 1 the Parcel ID for Bob’s land is 14 and would not be used for any other parcel in the County so that a unique link to the tax roll and other information can be made from this identifier. Note also in Hogan County all rights of way are tagged as 98 throughout the County and that all federal lands are tagged as 99. This means that parcel identification 98 and 99 may apply to multiple polygons, but they link to the same record in the tax roll and other systems. Note also that Parcel ID 12 in Example 1 applies to two polygons. This also does not violate the non-repeating rule because again Parcel ID 12 links to the unique tax roll information for that tax parcel. The multiple polygons may not always be contiguous as they are in Example 1, they could also be non-contiguous.
Parcel information changes frequently. When transactions are recorded, the tax roll is updated, and parcel maps are updated, if the geometry of the parcel changes. In some jurisdictions the updates replace the existing data and only the current parcels are kept. In other cases, a separate data set of historical or retired parcels is kept. Each change is tracked in a separate file. All changes are kept. In this approach a current parcel map is always available as well as a record of past transactions.
When are new parcel identification values are assigned? In Example 2, a new parcel has been created along with a new tax roll entry.
In this example, Mary has sold a portion of her land to Red. The land values have been apportioned accordingly and a parcel identification number has been assigned to Red’s land (12.1) and the parcel, parcel identification 12, has remained with Mary’s land.
The reuse of parent parcel identification numbers is a common practice in many jurisdictions. In these jurisdictions the parcel identification system helps track the parent-child relationships among the parcels. The other term for the parent-child parcel relationship is sometimes called remainder parcels. That is, Mary’s parcel is a remainder after the northwestern portion was sold. Remainder parcels also occur with subdivisions. In these cases only part of a parcel is included in the subdivision and there may be “remainder areas”.
There may be a concern about losing tax records. By keeping a parcel number active, that is reusing it and keeping it in the system, there is some assurance that the records for that parcel, perhaps past due taxes and other linkages, such as the link to the well and septic records, are not lost.
The reuse of the Parcel ID for parent or remainder parcels can create problems in tracking historical parcel information and in third party use of the parcel information. While the reuse of parcel numbers provides continuity for County systems, it can provide continuity for third party users as well. For example, if a mortgage company linked their records to a parcel identifier and that number was reused for a remainder parcel, the linkage to mortgage system, would exist, but it would be to a different area of land. If a jurisdiction or agency reuses parcel numbers, this will needs to be clear to the downstream users, and other information such as the area or the date of changes may be necessary to track changes.
Not all jurisdictions reuse Parcel IDs. Example 3 shows how the new parcel might be handled in an area where new parcel identifiers are assigned with every new parcel. In this example, the resulting new parcels have both been assigned a new number. The old record has been noted as inactive. This note of inactivity would probably be in a separate field, but for the purposes of explanation it is shown in the exempt field.
There are several outcomes of this process. The Well and Septic records that were tied to Parcel ID 12 are no longer linked to the active tax records. The former Parcel ID 12 has now become Parcel ID 16 and Parcel ID 17. At the time the new parcels are created, the Well and Septic Records could be updated to point to the correct Parcel ID. In this case a determination would need to be made as to which parcel gets the Well and Septic Records. In Example 3 this is relatively straightforward, but in actual practice it is not always this clear. The other problem is that the person or department maintaining the parcel records may not be responsible for the Well and Septic Permits. In this case editing the Well and Septic records would not be possible and another department would need to be notified of the changes so that the updates could be made.
In this case storing the X, Y and possibly Z or elevation value of the Well and Septic location could solve the changing Parcel ID problem. If the physical location of the permitted facility is stored, either in a table or on a map, then the link to parcel information can be done spatially. For example, a simple point in polygon analysis could be run to determine which parcel should be related to the permit. This process could be run any time a query is done so that the current information is always retrieved and the maintenance workload for linking these two systems is reduced.
The second question with generating new Parcel IDs is when to do it. That is, should a new Parcel ID be assigned anytime the geometry changes? If any parcel has a new legal description does it get a new Parcel ID? Example 3 is a clear example of assigning a new Parcel ID, but what if there is a boundary adjustment between two parcels? How much area change should occur before there is a new Parcel ID? Or, are new Parcel IDs only assigned when there is a new parcel created either by splitting an existing parcel or merging or combining two existing parcels? The answers to these questions may vary from place to place and thus create slight variations in what the parcel identifier means within a jurisdiction and how it can subsequently be applied.
In this example, Mary has sold a portion of her land to Red. The land values have been apportioned accordingly and new Parcel IDs have been assigned to Red’s land (16) and the remainder or parent parcel has also been assigned a new Parcel ID, (17). The record for Parcel ID 12 has been noted as inactive. In some systems a separate table may indicate which new parcels were created out Parcel ID 12 maintaining the parent child relationships.
Best practice is to reassign a new parcel identifier when a new parcel is created and keep a record of historical parent child relationships. The parcel mapper has to be aware of other systems that use the the parcel id to relink related records to the new parcel(s) as needed.
