The parcel data model in the parcel fabric
This topic applies to ArcEditor and ArcInfo only.
A parcel in the parcel fabric is composed point features, line features and polygon features. A series of individual lines close to form a polygon and each line has a from and a to point that are also the parcel corner points. Parcel points can have up to one line point and one control point. A parcel is always associated with one plan (record of survey).
The survey record (plans)
The parcel fabric provides a way to enter and organize parcel data based on the manner in which it was originally recorded (record of survey). Parcel data can be manually entered directly from a plan (survey record) or appended from a digital submission of a plan. Parcels are grouped in the parcel fabric by their associated plan, and the plan properties are maintained in a separate, related table.
The parcel data model
A fabric parcel always has the following geometric elements:
- Point features
- Line features
- Polygon features
Each parcel polygon in the parcel fabric defined by a set of boundary lines. The parcel polygon features are related to their lines in the parcel fabric.
Recorded dimensions from the plan or record of survey are stored as coordinate geometry (COGO) attributes on the parcel line in the parcel fabric. Recorded dimensions are derived from original raw survey measurements taken in the field. Dimensions include bearings, distances, and parameters for curved lines. Since dimensions are derived from survey measurements, they can have an associated accuracy. Accuracy can be derived from surveying equipment, date of survey, and so on. Each parcel line in the parcel fabric can have an associated accuracy. Generally, the more recent the recorded survey information (plan), the higher the accuracy of the parcel line and the higher the accuracy of the parcel.
Parcel lines in the parcel fabric also have line categories. The parcel in the diagram below has lines that can be categorized as roadfrontage lines and lines that can be categorized as connection lines.
Each parcel line in the parcel fabric is a two-point line, from one point to the other. These points are also the corner points of a parcel. The parcel lines features are related to their points in the parcel fabric.
A parcel point feature stores x,y,z coordinates, which are initially generated when parcel data is either migrated or joined to the parcel fabric. Control points are used in a fabric adjustment to improve the accuracy of these coordinates. Since point coordinates are a derived quantity, they are held as separate, transient attributes of a parcel point rather than the definition of the point itself.
A parcel point can also be a line point in the parcel fabric. A line point occurs when the corner point of a parcel lies on the boundary of an adjacent parcel, but does not split the boundary. The adjacent parcel will have a line point lying on its boundary instead of the adjacent parcel corner point. In this way, a parcel boundary is not split or broken by an adjacent parcel corner point in the parcel fabric. This is important for preserving the recorded information. A parcel boundary should be represented with a single bearing and distance and not with separate bearings and distances if an adjacent parcel corner point is lying on or "splitting" the boundary line.
Modeling parcel relationships
Just as relationships exist between parcels, lines, and points in the parcel fabric, relationships exist between parcel features and other parcel fabric data elements such as between parcels and plans. The following list summarizes the relationships between parcel features themselves and between parcel features and other tables:
- A parcel polygon is related to many lines.
- A parcel line has two endpoints.
- A parcel line is related to only one parcel, resulting in two lines representing common parcel boundaries.
- A parcel point is related to one control point.
- A parcel point is related to one or more lines.
- A line point is related to one or more parcel polygons.
- A line point is related to one parcel line.
- A parcel point is related to one line point.
- A parcel polygon can have many line points.
- A parcel polygon is related to one plan.
- A parcel can have one or more historic parcels (lineage).
- A parcel point can have one or more adjustment vectors (from a fabric adjustment).
- A parcel polygon has one accuracy category.
- A parcel line has one accuracy category.