Curves in the Parcel Fabric

There are many ways in which the Parcel Fabric differs from our current mapping concept, some of them are obvious, such as the tools we use and the way we store land records data. But there are also subtle differences that we need to understand to make the most of the Parcel Fabric - We need to especially recognize that the Parcel Fabric stores curves differently.

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Feature Class Curves

Within a standard feature class, the curve is a variation on a single line vector. Albeit, the curved line has specific properties that define the amount that the curve is "bent". In fact, when we interact with the curve using the standard editing tools, we are actually just changing those specific properties that define the curvature.  

Because of the way the curve (arc) is stored, there are many tools in ArcGIS to help you define those specific properties to cause a curve to pass through start, middle and end points (arc function) or through specific endpoints (endpoint arc function), tangent to a previous course (tangent arc) or even a bezier curve (bezier). 

A Curve as defined in the Parcel Fabric

A Curve as defined in the Parcel Fabric


Parcel Fabric Curves

However, within the Parcel Fabric, curves are constructed and stored as geometric definitions and the actual point of curvature (PC), point of termination (PT), the radius point (RP) and radius lines are constructed and stored. These points and lines define how the curve is drawn. Interestingly, because the actual arc of the curve is constructed within the Parcel Fabric, you cannot join or link to the actual curve - you must join or link to the defined points (Point of Curvature, Point of Termination or Radius Point.)

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The implications of this difference in the way curves are stored are important to understand. For example, if two curves are stored in the Parcel Fabric and are supposed to be concentric and there are any variations in the location or geometry stored with those curves, they will create differing points and will not be drawn as concentric. Instead, there will be two different points stored as illustrated to the right. In this example, the two curves were stored and there was a difference in the radius length stored ( this was not necessarily an error, this difference could have been simply a rounding error on the original information.) But, having these two points stored as different values will result in the curves not being drawn concentrically. 

To remedy this issue, you must force those two points to be stored as one.  To accomplish this, you use the Mean Points tool in the Parcel Editor Toolbar. 

The Mean Points tool in the Parcel Editor Toolbar

The Mean Points tool in the Parcel Editor Toolbar

Dragging a box around the points to be "meaned" (averaged) will move the points together and result in having the curves drawn as concentric, even if they have differing COGO information stored in their respective geometries.

Remember, within the Parcel Fabric, the actual joins to points and linepoints is critical to how your data is drawn.  Be sure to check to make sure the points are joined correctly and that all three points in the curve (PC, PT and RP) are correct.