How much does each city increase the cost of social policies?

In Civilization 5, each city you build increases the cost of new social policies by some percentage, based on the current map size.

This question mentions +30% for duel sized maps. I'm assuming this is correct?

What are the percentages for other map sizes?

Solution 1:

This is taken straight from the XML files included with Civ V: (Updated for the June 2011 patch, where all of them were reduced by 50%)

 <Type>WORLDSIZE_DUEL</Type> 
  <NumCitiesPolicyCostMod>15</NumCitiesPolicyCostMod> 


  <Type>WORLDSIZE_TINY</Type> 
  <NumCitiesPolicyCostMod>15</NumCitiesPolicyCostMod> 


  <Type>WORLDSIZE_SMALL</Type> 
  <NumCitiesPolicyCostMod>15</NumCitiesPolicyCostMod> 


  <Type>WORLDSIZE_STANDARD</Type> 
  <NumCitiesPolicyCostMod>15</NumCitiesPolicyCostMod> 


  <Type>WORLDSIZE_LARGE</Type> 
  <NumCitiesPolicyCostMod>10</NumCitiesPolicyCostMod> 


  <Type>WORLDSIZE_HUGE</Type> 
  <NumCitiesPolicyCostMod>7.5</NumCitiesPolicyCostMod> 

So it's 15% for all but the largest two map sizes.