The 9×9 block is a step up from just having a single long winding road going through the entire city. At least with the 9×9, you have defined city “sections”.
The rationale for this block is the efficient use of the fountain radius. In central and northern provinces, ie. any scenario where that the ground is green as opposed to milky-white, the fountain radius is 4 tiles, hence a block that measures 9 houses long by 9 houses wide, can be serviced with a single fountain at the center. Put a road outside of the houses, and gardens or medium statues inside (to raise desirability). There is plenty of space across the road from the houses, for all the service buildings to go.
While using the 9×9 block does simplify the process of city planning, it does however carry with it the drawback of unpredictability, that is, the 9×9 block does not exist in isolation, it needs to be connected to other blocks. When you connect a lot of 9×9 blocks together, you are forced to subject yourself to the whims of Caesar III’s path-selection algorithm for its walkers.
While the 9×9 block is a simple concept, it can nonetheless prove to be extremely effective in the hands of an expert player, as evidenced by the Caesar III Olympic Games solutions of Zack Caophil.
The default 9×9 block (non-desert maps)