Used to redefine true North (by default, the design plane y-axis) to any direction in the design plane for precision input key-ins and computing direction measurements. This direction is used by the product when displaying angles or dimensions in bearing mode. Additionally, it is used to calculate the direction of the Sun for Solar Lighting when rendering a view.
In order to Define North in a design file, it is necessary to know the true direction of a line between two points in the design. The line between the points need not point North, but can be in any direction, as long as the direction is known.
For example, assume you have a design with a shape that bounds a section of property, but the boundaries were digitized at an arbitrary rotation. Also, assume that you have the deed, so you know the bearing of at least one of the boundary lines. In order to label the boundary lines correctly with the LABEL LINE key-in, it is necessary to use Define North so that the bearing labels match those on the deed. Then, by snapping to the line with a known direction and entering the known direction (from the deed), it is possible to match the map coordinates to those on the deed.
To define North for Solar Lighting, it is usually easier to use the settings in the Solar Position section of the Light Manager dialog. This gives you various options for defining the direction for North.