About COGO descriptions

This topic applies to ArcEditor and ArcInfo only.

The geometry of a straight line can be described using a direction and a distance. Similarly, you can describe the geometry of a circular arc with parameters such as arc length, chord distance, radius, central angle, and tangent length.

COGO lines

A COGO line is a feature that is either completely straight or completely circular. If the feature has any vertices between the endpoints, every vertex must fall within the x,y tolerance of a line or curve created between the endpoints. Only these types of line features have valid COGO descriptions.

COGO lines can be created a number of ways. For example, you can create them when you use the following:

• Traverse window
• Offset Line window
• Construct 2-Point Line window
• Cul-de-sac command
• Split Into COGO Lines command

Required COGO fields

The table below lists and describes the required table fields to maintain COGO attributes.

Field name	Description	Field alias	Format
Direction (or Angle)	If the feature is straight, this is the direction of the line. If the feature is a circular arc, this is the direction of the chord line. The field is named either Angle (to be compatible with ARC/INFO coverages) or Direction (if you use the Create COGO Fields command).	COGO Direction	Text Length=12
Distance	If the feature is straight, this is the distance between the endpoints. If the feature is a circular arc, this is the distance along the chord line.	COGO Distance	Text Length=10
Delta	The central angle formed between the endpoints of the curve and the center point. When editing in ArcMap, this is typically referred to as the Angle.	COGO Delta	Text Length=10
Radius	The length from the center point to the curve.	COGO Radius	Text Length=10
Tangent	The distance between the endpoint and the point of tangency. The point of tangency is determined by intersecting a perpendicular line from each of the endpoints of the curve.	COGO Tangent	Text Length=10
ArcLength	The length along the curve. When editing in ArcMap, this is typically referred to as Arc.	COGO ArcLength	Text Length=10
Side	The side on which the center point of the circular arc is located.	COGO Side	Text Length=1

Outputting COGO descriptions

Specific COGO commands in ArcGIS can store the COGO descriptions you enter as attributes on COGO line features. The values added include the direction and length for straight features and curve characteristics such as chord distance, chord direction, arc length, radius, tangent length, and side. The current direction type and angular units for the ArcMap editing environment are used when populating these attributes. The map's current coordinate system linear units are used when populating distance attributes.

The COGO commands in ArcGIS should be used to update line features to maintain COGO attributes. For example, to split a line, use the Proportion tool on the COGO toolbar so the COGO attributes will be automatically updated. Using the Split command or tool will not update COGO attributes.

The following commands write COGO descriptions to the COGO attributes of a line feature class:

• Merge—Merges two or more selected features into a single feature. If you select lines that are entirely straight or curved and they have COGO fields, you can update the COGO descriptions.
• Traverse window —Creates a feature from a series of COGO descriptions that form an open or closed traverse.
• 2-Point Line window —Creates a COGO line feature from a COGO description.
• Cul-de-sac —Creates a symmetrical or asymmetrical cul-de-sac from a street centerline.
• Proportion —Splits the selected line into a number of segments.
• COGO Report —Lists the COGO descriptions for lines and features in the map.
• Split Into COGO Lines —Splits the selected lines at every vertex and updates the COGO fields.
• Update COGO Attributes —Calculates COGO descriptions for selected lines from the feature geometry.