The Map Parameters Tab.

This very important screen handles the information stored in the world_gen.txt file and also allows you to set which maps should be generated by PerfectWorldDF. To view and edit these fields, first you must import your world_gen.txt file from your df_xx_xx\data\init folder by selecting the File menu and selecting 'Import world_gen File'. To save any changes you make to the world_gen.txt file, you must select the File menu again and select "Export world_gen File'. Nothing is ever written to the world_gen.txt file automatically.
Map Paramters Screenshot

The 'Parameter Set' group box contains controls to add and remove parameter sets and also to change the map sizes. To select a parameter set to view, use the list box labled 'Name:' and select the desired parameter set name from the list.

To add a new parameter set, select a param set that you want to copy and then type a new name into the list box and press the 'Enter' key. This will create a new param set called by your new name.

To delete a parameter set, first select the param set you wish to delete, and then press the 'Delete Param Set' button.

You may change the map size for the selected parameter set, but this will delete any pre-set map data that was stored in the world_gen.txt file. Also, many fields in the param set (marked in light green) will be automatically resized by PerfectWorldDF. This should be desireable in most cases but not necessarily. Have another look at the green fields if you resize the map in this way to make sure they are reasonable.

To use the maps generated in PerfectWorldDF you must select the check boxes for each map you want to generate. This action will erase some of the map rejection criteria fields and mark them in red. You may go back and change those values but usually you don't want this rejection criteria for PW generated maps. Any pre-set map data stored in the param set before you selected the map for PW generation will be overwritten upon exporting to the world_gen.txt file.

For information regarding the individual parameter fields inside of world_gen.txt, most of what you need can be found in the Dwarf Fortress Wiki.