Inference is a constraint mode that uses the current snap settings to snap the pointer to inferred geometric relationships between the current vertex and existing feature geometry. Inference 
is turned on or off on the status bar at the bottom of the active map.
Caution:
Inference is primarily intended for drawing rectilinear shapes that represent objects in built environments. Using the Inference button with dense vertices can degrade map performance.
To turn on and use inference constraints, complete the following steps:
- On the status bar at the bottom of the active map, hover over the Inference button until the pop-up menu appears and turn on the Inference toggle button.
- On the ribbon, click the Edit tab, and in the Features group, click the drop-down arrow next to the Snapping button, and enable one or more of the snap agents:
Edge
Snap to inferred line extensions displayed as straight lines.
Intersection
Snap to inferred intersections of two or more lines or edges.
Point
Snap to inferred perpendicular intersections displayed as squares.
Vertex
Snap to inferred distance radial intersections displayed as circles.
- On the Home tab, click the Map Notes button.
- On the drop-down menu, click the Create Map Notes button.
- In the Create Features pane, click the Line Notes tool or Polygon Notes tool.
- Click the map to create a vertex.
Create at least one segment if you are using inference to initially constrain the pointer to feature geometry you are actively drawing.
- Hover over a segment of a nearby feature or the feature geometry you are actively drawing.
The segment being analyzed briefly flashes and the related constraints you can snap to are displayed.
- Hover over the related constraints, allowing the enabled agents to provide feedback, and click the pointer to snap the geometry to the constraint.
The perpendicular constraint appears as a square and represents the extended intersection of two segments.
- Click Finish
on the editing toolbar, or press the F2 key to finish the feature.