These settings specify snap strength for different objects on the page and shape extensions for additional snap-to points (including the angles for which shape extension lines appear).
Shape extension options
Use these options to specify additional snap-to points. Shape extensions work with the Line 
Alignment box extension
Snaps the pointer to a line extended from a shape's alignment box.
Center alignment axes
Snaps the pointer to a line extended from the center of a shape's alignment box.
Curve interior tangent
Snaps the pointer to a line tangent to a curve. Drag the pointer over an arc segment until you see a dotted line showing the tangent. Drag the pointer along the dotted line until the line you are drawing turns red.
Segment endpoint
Snaps the pointer to the endpoint of a line segment or arc segment. A line segment can include line shapes and lines used to create the sides of a polygon.
Segment midpoint
Snaps the pointer to the midpoint of a line segment or an arc segment. A line segment can include line shapes and lines used to create the sides of a polygon.
Linear extension
Snaps the pointer to a line extended from the endpoint of a line segment. Move the pointer over a line segment until you see a dotted line extending from the nearest endpoint, and then drag along the dotted line. A line segment can include line shapes and lines used to create the sides of a polygon.
Curved extension
Snaps the pointer to a curved line extended from the endpoint of an arc segment or freeform curve. Move the pointer over an arc segment until you see a dotted line that shows what the arc would look like as an ellipse, and then drag along the line. For freeform shapes, extends the curve at the endpoint that you're near.
Endpoint perpendicular
Snaps the pointer to a line perpendicular to a line segment or arc segment endpoint. Move the pointer over a line segment or arc segment until you see a dotted line extending from the nearest endpoint, and then drag along the line. A line segment can include line shapes and lines used to create the sides of a polygon.
Midpoint perpendicular
Snaps the pointer to a line perpendicular to the midpoint of a line segment or arc segment. Move the pointer over a line segment or arc segment until you see a dotted line extending from the midpoint, and then drag along the line. A line segment can include line shapes and lines used to create the sides of a polygon.
Horz line at endpoint
Snaps the pointer to a line horizontal to the endpoint of a line segment or an arc segment. Move the pointer over a line segment or arc segment until you see a dotted line extending from the endpoint, and then drag along the line. The dotted line is horizontal to the screen, not to the page, so it is not affected by page rotation. A line segment can include line shapes and lines used to create the sides of a polygon.
Vert line at endpoint
Snaps the pointer to a line vertical to the endpoint of a line segment or an arc segment. Move the pointer over a line segment or arc segment until you see a vertical line extending from the endpoint, and then drag along the line. The dotted line is vertical to the screen, not to the page, so it is not affected by page rotation. A line segment can include line shapes and lines used to create the sides of a polygon.
Ellipse center point
Snaps the pointer to the center of an ellipse.
Isometric angle lines
Snaps the pointer to lines extended from the endpoint of a line segment or arc segment at the isometric angles specified in the Isometric angles (deg) box. Move the pointer over an endpoint until you see a dotted line extending from the vertex, and then drag along the dotted line. This option is most useful if you are creating an isometric drawing.
Isometric angles (deg)
If Isometric angle lines is selected under Shape extension options, specifies the angles for which shape extension lines appear, such as 30, 60, and 90 degrees. You can enter up to 10 angles (in degrees), separated by commas. This option is most useful if you are creating an isometric drawing. A line segment can include line shapes and lines used to create the sides of a polygon.
Snap strength
Use these settings to specify in pixels how far the rulers, grid, guides, points (connection points, shape vertices, shape handles), shape geometry, or shape extension lines pull when snapping is turned on.
