It makes sense that by bombarding a city you might decrease its population. It doesn't make sense that you can decrease the size of the city: buildings might be converted to rubble, but that rubble doesn't just disappear.
A common tactic is to bombard cities that are size 12+ until they are smaller in order to decrease the defensive bonus the enemy gets. However, I figure the defensive bonus is terrain based, i.e., the sprawl of buildings in the city gives the defenders plenty of cover. Piles of rubble give cover pretty well, too, so I think large cities should retain their defensive bonus even if they've been bombarded enough to lose significant population.
Also, it just looks silly to see a the metropolis graphic suddenly be replaced by the city graphic (or the city replaced by a town) just because of bombardment. C3C or PTW (can't remember which) introduced ruins that appear when a city is destroyed. Why not also have partially ruined cities. What I mean is this: when a metropolis is bombarded below 12 population, instead of being replaced by the city icon, it is replaced by a different metropolis icon in which some of the buildings are just piles of rubble. Same thing for dropping below size 6: have a modified city icon showing the damage instead of just using the town icon. These new icons wouldn't be hard to implement, and they would give a visual clue that, even though a city had less than 12 population, the city itself was still large and still gave the defenders the higher defensive bonus.
A common tactic is to bombard cities that are size 12+ until they are smaller in order to decrease the defensive bonus the enemy gets. However, I figure the defensive bonus is terrain based, i.e., the sprawl of buildings in the city gives the defenders plenty of cover. Piles of rubble give cover pretty well, too, so I think large cities should retain their defensive bonus even if they've been bombarded enough to lose significant population.
Also, it just looks silly to see a the metropolis graphic suddenly be replaced by the city graphic (or the city replaced by a town) just because of bombardment. C3C or PTW (can't remember which) introduced ruins that appear when a city is destroyed. Why not also have partially ruined cities. What I mean is this: when a metropolis is bombarded below 12 population, instead of being replaced by the city icon, it is replaced by a different metropolis icon in which some of the buildings are just piles of rubble. Same thing for dropping below size 6: have a modified city icon showing the damage instead of just using the town icon. These new icons wouldn't be hard to implement, and they would give a visual clue that, even though a city had less than 12 population, the city itself was still large and still gave the defenders the higher defensive bonus.