The ruleset is just the default nations.ruleset, only slightly edited to get rid of Dúnedain and Mordors, and further rearranged (and shortened) to fit the large-scale maps of the world presented here. It is supposed to be used with the definitions of default nations in the data/nation directory of the standard FreeCiv installation.
The correspondence between the nations and birthplaces in the above mentioned maps is subject to several limitations, since not all desirable nations (e.g. the Maori) are available in the default set, and not all available nations can be put in its native place (Europe cannot contain 20 nations). The nations were therefore placed partly to their native places, partly to lands they colonized (if no native nation is available in the default set).
The list of nations can easily be altered (if you prefer to have e.g. Hungarians instead of Czechs in your game) or expanded (if you want to have some random positions) by simple "de-commenting" the eliminated nations in the ruleset file.