To draw lines freely, you are allowed to draw beyond borders. For that purpose, the following steps will be implemented. Create layers of hair, face, and lines (other than hair and face) separately. This makes it easy to adjust where lines intersect. Draw sequentially from a part close to a camera. Select parts where drawing is finished with [Auto select] tool, then [Selection] menu[Invert]. This keeps lines away from borders, so you can draw lines freely. Make line drawing of a background. Draw from a front part in the same way as a character. Draw with freehand except for the parts where a perspective ruler is applicable. Put a dense gray color on the character to make it visible. To make it easy to manage layers, create different layer folders for a character and a background and store layers to each folder. To draw parts in the back, click [Create copy of currently selected sub tool] icon lower right of [Sub Tool] pallet, register [Mapping pen] with its brush size 2 pixels smaller, and use the pen. Add thin lines such as scale and pattern to line drawing of a character by creating a new layer “Thin line”. I am doing this step here, but it was supposed to be done for line drawing of a character. Draw lines roughly intersecting each other with a ruler. By selecting [Eraser] tool[For vector] and [Vector eraser][Erase up to intersection], you can erase parts outside of crossing lines. When you draw lines over complicated ones, you can erase only the lines with [Vector eraser][Overall line]. For a background, thickness of lines is often changed to add perspective. (In this case, front lines are with thick lines while back lines are thin.) For a vector layer, you can change thickness of lines after drawing them. You better use a raster layer for a square shape such as line drawing of a character. You cannot use “Fill” for a vector layer. There are features for a vector layer such as unique fade out. Source.