Creating a curve through start, middle, and end points (Arc)

Arc helps you create a segment that is a parametric (true) curve. Instead of being made of numerous vertices, a parametric curve has only two vertices as endpoints. You might use Arc to digitize a cul-de-sac, using an aerial photo image as a backdrop.

Arc creates a curve through the starting, middle, and ending points you specify. Click to place the start point, click again to place the midpoint of the curve, then click a third time to place the endpoint of the arc segment.

1. These steps can be used to create vertices in either lines or polygons:

   To create a vertex in a line	Click a line feature template in the Create Features window and click the Line tool .
   To create a vertex in a polygon	Click a polygon feature template in the Create Features window and click the Polygon tool .

2. Click Arc on the Editor toolbar.
3. Click once to establish the start point of the arc.

   A vertex is created.

4. Click once to establish the axis of the arc. This is the invisible point through which the curve passes.

   After you have clicked the second point to set the axis, you can press R to set the radius value. Press TAB to cycle through the possible curve solutions.

5. Click once to establish the endpoint of the arc.

   A segment that is a true (parametric) curve is created.