According to the information in the graphs, which revenue source supplied local governments with the largest percentage of funds

The purpose was for Hammurabi (sometimes written "Hammurapi") to set down a reasonable and unchanging set of laws that addressed common problems in his kingdom. The code was especially important because, up until that time in history, there really were not any wide-spread laws that unified such a large group of people.
Before this, justice in many places would have been in the vigilante style, i.e. if someone in your small village steals your cow, it's most likely up to you and your family to go find it and then punish the perpetrator. The punishment for stealing might have been being lashed with a whip, for example, in one town and yet five miles away in another town the punishment was having a hand cut off. Under the code, everyone was eligible for the same punishments and fines no matter where they went. With one law from the king on down, there was less risk of being hanged or stoned for something relatively minor, or starting a never-ending feud between families over a disputed punishment