When drawing the general layout in automobile design, we must first determine the baseline of drawing, and ask why there are five baselines, all of which are indispensable.

After the overall scheme is determined, the relevant calculation of the overall layout of the vehicle should be carried out, and the general plan of the vehicle should be formally drawn and arranged on the basis of the sketch of the overall scheme layout and the matching of each assembly. The general layout of the vehicle includes side view, top view, front view, necessary section layout and local layout. In the process of drawing the general layout of the whole vehicle, it is necessary to cooperate, adjust and confirm the overall size, structure, layout form, connection mode, the relationship between the assemblies, the layout requirements of the control mechanism, the structure and layout requirements of the suspension, the layout and fixation of the pipeline, and to facilitate assembly and adjustment at any time. Therefore, there must be five datum lines to draw the general plan.

Plane line on the frame: the plane of the long upper wing surface of the longitudinal beam or the upper edge surface of the middle floor of the load-bearing car body or the projection line of the side beam in the side (front) view. As a datum line (face) for dimensioning vertical dimensions.

Front wheel center line: the plane passing through the center of the left and right front wheels and perpendicular to the plane line of the frame, the projection line on the side view and the top view. As a datum line (face) for dimensioning the longitudinal dimension.

Automobile centerline: the projection line of the vertical symmetry plane of the automobile on the top view and the front view. As a datum line (face) for dimensioning transverse dimensions.

Ground wire: the projection line of ground plane in side view and front view. Datum marked with dimensions such as car height, approach angle, departure angle, ground clearance and cargo platform height.

Vertical line of front wheel: the projection line passing through the center of left and right front wheels and perpendicular to the ground in side view and top view. As a reference line to mark the wheelbase and front suspension of the car.