Maybe you guys could answer a question for me: It may be the single reason why I don't play so hot. Here it is: The city screen shows that you only "work" a certain number of tiles. Is there any point in developing tiles beyond that number? I think if there are resources like iron on the tiles, you do get the resources, but what if it's food. I've been developing all resources and I may be wasting my time doing so.
It looks as though when you develop a tile your city isn't working, like with an iron mine, you would get the iron but not the hammers and foods of the tile itself.
Ha..I could write a thesis on all this. First, let me just say that Civ IV is a pretty complex game. I'm not sure what exactly your experience level is with the game, but just understanding a few basic things can help your game immensely. And yeah, I've seen folks actually play this game for many years...incorrectly. Of course, folks play a game like IV for different reasons and in different ways - such as very casually, role-playing, up to your super-pros. Regardless, the point I'm making is having just a core understanding of the mechanics can help any player regardless of style. A great place to learn the game is over in the Strategy & Tips forum here:
S&T
Lost of good folks there that like to help out players, and there are fun games to play, share and learn.
So anyway, I'll try to answer your questions as best I can and apologize if I go over concepts or mechanics that you know already.
A city has what we term a Big Fat Cross (BFC). I'm posting a random image I have stored to demonstrate:
I wish a had a pic at moment that I could mark up for you, but basically the BFC is all the tiles lit up that you see, minus 2 tiles that are current stolen by another city sharing some of those tiles (that can be manipulated by the way)
Aksum is Size 6 and you see 6 citizens (white circles) working different improved tiles in this city such as pigs, sheep, gems, gold, a flood plain cottage and an improved forest spice tiles. The city is basically working the best tiles available at the moment. I have a library so I could also move 2 citizens to scienstist specialists and start producing a great scientist.
Working those various tiles provides the yields those tiles produce as seen on the map. You get whatever food, hammer or commerce those tiles produces. That information is actually displayed in the city screen UI, including any modifiers like a library in this case.
Having "access" to a "resource" like iron is separate from tile yield. For example, access to iron lets you build metal based units like Swordsman. (That access is basically empire wide at least as long as cities are connected) A city with an improved iron resource in its BFC can work that tile for the hammers it provides which is local to that city. Like a grassland iron would produce 2F4H or a plains iron would produce 1F5H. The city only receives that yield if a citizen is actually working that tile.
So hopefully that makes some sense for you.
Now, you also mention something about "improving all resources". I think you may be referring to resources that lie outside any of your cities' BFCs, such that no city can actually gain the yield from that tile since no citizen is able to work the tile. Well, extra copies of resources can be traded, so there is certainly no harm in improving a resources that cannot actually be worked. In some cases it might be a resource like a happy resource that you want access to anyway. (Note: You would still need road/river access to that resource) If by "food", you mean a food resource like wheat, rice, deer (etc)....well, they do provide health and they can be traded too.
However, just improving a random tile (no resource) outside an BFC does nothing - unless you plan to settle the area later.
I hope that helps, and apologize if I misunderstood the context of your questions.