For most applications, it's important that objects rendered with GDI functions are identical whether they appear on a VGA display, an EGA display or a high-resolution laser printer. For example, a geography application may require a scale of 1 mile : 1 inch whenever it displays a map and a drawing/painting application may require a 1 centimeter grid whenever it displays its “canvas”. If your application falls into this category, it should take advantage of the predefined mapping modes. (Unless, of course, the predefined mapping modes do not provide the required units, in which case you should use the MM_ISOTROPIC or MM_ANISOTROPIC modes). The following list contains the constant associated with each predefined mapping mode and describes the corresponding drawing-units:
| Mapping-Mode Constant | World-Space Units |
| MM_HIENGLISH | drawing units are a multiple of .001 inch |
| MM_HIMETRIC | drawing units are a multiple of .01 millimeter |
| MM_LOENGLISH | drawing units are a multiple of .01 inch |
| MM_LOMETRIC | drawing units are a multiple of .1 millimeter |
| MM_TWIPS | drawing units of a multiple of .0006944 inch |
Once you determine the units required by your application, you should select the appropriate mapping mode by calling the SetMapMode function and supplying the corresponding constant.