Economy

A nation's economy is its most important feature. Your economy determines your income, and thereby indirectly the speed with which you can build military units and improvements, and how many you can afford to maintain. And therefore, through improvements, it also determines how quickly you can extract and manufacture goods, and how quickly your nation can advance.

Natural Income

Your income is determined by your economic advancement – mostly related to the technologies you have researched. Specifically, your income per production receives a 1% bonus for every point your Economy stat gains.

Each tile has a natural production, which reflects how fertile and supportive of people the tile is. The best tiles are those with a small temperature range and a pleasant warmth, with desert or frozen tiles giving much lower values. The production affects the amount of working citizens a tile contains, and it also affects the size of military you can have on a tile and still produce any income. You can increase the production on a tile by researching Agriculture; each point gives you a 1% bonus to the production of each tile you own.

Costs

Taken on its own, each tile has no cost apart from the production that is sacrificed for military units. So if you have only unmodified tiles, you will be making money and not spending any. However, any improvements you may choose to build (apart from the basic Resource Collection of surface resources) will have an upkeep cost, which may be higher than the income from that tile.

In addition to improvement costs, which are associated with particular tiles, most military units (whether garrisoned on a tile or as part of a brigade) cost money and/or resources to maintain. If you have too large an army, you may find yourself with cashflow problems.

Balance

It is important that your income is higher than your costs. If you have insufficient money to keep an improvement going, it will eventually become unusable and disappear. If you can't afford the upkeep on a military unit, it will be disbanded immediately – so becoming economically troubled can make you an easy target for invaders. You can see a summary of your costs and income from the Nation Manager. If you need to reduce costs, you can decommision some of your improvements, or choose smaller brigades of less expensive military units. Or, if the price is right, you could build extraction improvements and sell resources through the market.