Of the six predefined mapping modes, one is device dependent (MM_TEXT) while the remaining five (MM_HIENGLISH, MM_LOENGLISH, MM_HIMETRIC, MM_LOMETRIC, and MM_TWIPS) are device independent.
The default mapping mode is MM_TEXT. One logical unit equals one pixel. Positive x is to the right, and positive y is down. This mode maps directly to the device's coordinate system. The logical-to-physical mapping involves only an offset in x and y that is defined by the application-controlled window and viewport origins. The viewport and window extents are all set to 1, creating a one-to-one mapping.
If your application displays geometric shapes (circles, squares, polygons, and so on), you may want to choose one of the device-independent mapping modes. For example, if you are writing code to provide charting capabilities for a spreadsheet application and want to guarantee that the diameter of each pie chart is 2 inches, you can choose the MM_LOENGLISH mapping mode and call the appropriate functions to draw and fill the chart. By specifying MM_LOENGLISH, you guarantee that the diameter of the chart is consistent on any display or printer. If you were to choose MM_TEXT instead of MM_LOENGLISH, a chart that appears circular on a VGA display would appear elliptical on an EGA display and would appear very small on a 300 dpi (dots per inch) laser printer.