To help draw objects in a plan view, the program infers a linear geometric alignment between the position of your mouse cursor and previously drawn columns. This inference is visible as dashed lines that are always parallel to the axes of the current coordinate system as shown in the drop-down list in the lower right-hand corner of the program. This inference works only with Cartesian coordinate systems, including User Coordinate Systems (UCS), and will not work with cylindrical systems. The type of inference depends upon the object being drawn:
Columns and Beams: When in the column or beam draw mode, orthogonal dashed inference lines parallel to both axes of the current coordinate system will be shown connecting the mouse cursor location with the “from” column. To encourage a column to be identified as a “from” column, simply pause the cursor over the column. Additional inference lines may appear if the mouse cursor aligns with other columns in addition to the “from” column. Optionally, the orthogonal inference lines may be converted to a single radial line by holding down the Shift key.
Slabs: When in the slab draw mode, any time that your mouse cursor lies along a line that both intersects a column location and is parallel to one of the current coordinate system axes, a dashed line will appear connecting the mouse cursor to the column. Two orthogonal dashed inference lines may appear if the mouse cursor is positioned such that it forms the vertex of a right angle with two columns.
Draw menu > Snap Options