Map sizes and coordinate controls are stored in an internal coordinate system designed to ensure that maps will display satisfactorily on any device whatever the default font and resolution. From 4.616 you have some additional control over this.
The internal coordinate system is based on assigning the size of a standard character in the default font as 16 internal units horizontally and 32 units vertically. (Typically characters are usually about twice as tall as they are wide). At run time the terminal manager calculates the actual size to be used for this character based on the chosen default font.
The height is the external lead in + the actual character height. This is called the y_factor.
The width is the maximum of the following three quantities: the reported average width, the width of "n", the width of "8". This is called the x_factor.
(For narrow spaced maps the terminal manager only takes the maximum of the average width and the width of 8). (This is called narrow_factor)
From 4.616 these factors are modfied as follows: if isometric=1 is set in then the terminal manager adjusts x_factor and y_factor so that a rectangle that has an equal width and height in internal units appears as a square on screen.
It does this by increasing one or other of x_factor and y_factor as required. If x_factor is increased controls will appear slightly larger horizontally, if y_factor is increased they will be larger vertically. Font sizes are unchanged. The default for isometric (its value if it is missing from the DP4 configuration file), is 0, however it is set to 1 in the issued DP4 configuration file. The value of isometric will only have an effect if your default font is NOT twice as high as it is wide. Note that the System font (at least on US Windows) is isometric anyway. Setting isometric=1 when you use another font (such as MS Sans Serif) as the default font may change the size of maps on screen. Doing so will ensure the aspect ratio of printed maps is the same as display maps, though this will only be necessary if there is significant difference in how Windows realises the font when printing from on screen.
From 4.616 you can specify values for x_factor and y_factor in the DP4 configuration file. The only time you would be likely to need to do this is if you wanted to use a default font that was slightly smaller than your desired x_factor and y_factor. For example if you design an application to run full screen at 640*480 you can ensure it will also run full screen at 800*600 resolution, whether the user chooses "Large" or "Small" fonts by specifying x_factor=10, y_factor=20.
If you increase (or decrease) the size of maps by changing the x_factor or y_factor explicitly, or by changing the default font you use to one that has a different x_factor or y_factor, text may not fit nicely into controls. For example, text is usually aligned to the top of controls, and if the size of controls is increased too much this can become obvious. From 4.620 you can also adjust the size of text in fonts, using the new x_inch and y_inch settings. These settings change the number of points per logical inch from the default value of 72. A smaller value makes your fonts smaller. For full details see the description of the x_inch setting.
From 4.620 DP4 ignores the x_factor and y_factor settings when printing with DFPRINT. Originally x_factor and y_factor where used to that maps would print at the same logical size as they appear on screen. However, it is frequently the case that the size of maps on screen needs to be increased, because Microsoft Windows deliberately does not report the screen resolution correctly, whereas it is very unusual for printer resolutions to change much.
If required you can control all these settings for maps printed with dfprint using dfprint_x_factor,dfprint_y_factor, dfprint_x_inch,dfprint_y_inch.