There isn't one - basically, grab every important resource you see in sight, that's the path to victory.
The way the resource system works, nearly all buildings that you unlock through research provide modifiers to the base income, and without a resource attached to the city, most of those base income levels will be 1 or 0. You can't boost food production without a food resource to boost, same for metal (and I'm not even sure if there are any crystal boosters).
There are a few buildings that do give gold, arcane, or tech knowledge, but they're fairly rare.
So in that respect, large cities are the only way to play Elemental, as you need the multipliers on your base resource gain to maintain a high level of resource output, and you can't put down the buildings that give those multipliers without a city that has been leveled up.
Supposedly there's some sort of city maintenence cost (I've seen buildings that purport to reduce it), but I wasn't able to locate what the maintenence cost actually _is_. Presumably it's there to give a gold penalty to building up lots of small cities solely for an area of influence (with the overpowered teleport spell, having 'waypoint' mini cities is useful/critical on larger maps).
Mostly, your city size/expansion is limited by food, rather than gold - you can't actually grow a city without food, so if your food income is too low, you won't be able to grow new cities, which in turn limits your ability to get dispersed resources into your area of influence.
