Health

§ A City's health affects the rate at which the city accumulates Food, and thus the rate at which the city grows (or starves). A healthy city will grow larger, faster, while an unhealthy city will languish.
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Factors Affecting Health

§ Many factors affect a city's health: the Land around it and its access to water and Resources, the city's population, its Buildings and Wonders, and the Civics that the civilization is running. Health-giving objects provide one or more "positive health points," displayed as little red crosses in white circles. Unhealthy objects provide one or more "negative health points," displayed as green unhealthy faces.
§ Further, a city's population can be a major source of negative health points. The larger a city is, the more positive health points it needs to cancel out its population-based unhealthiness. Certain buildings, especially ones dealing with industry, will also add unhealthiness. And, finally, if you engage in any unpleasant nuclear exchanges with your neighbors, the resulting fallout can be extremely unhealthy for the few battered survivors.
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Determining a City's Overall Health

§ If a city has as many or more positive points as it has negative points, that city is healthy. If the city has fewer positive points than it has negatives, that city is unhealthy. The healthy and unhealthy icons are displayed at the top of the city screen, above the happy and unhappy face icons.
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Effects of Unhealthiness

§ A city loses one food for each point of excess unhealthiness. In other words, if a city has two positive health points and four negative points, the city will lose two food each turn. This will at the least slow the city's growth, and at the worst cause the city to Starve.
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Correcting Early Bad Health in a City

§ There are a number of steps you can take to improve the health of your cities.
§ Site the City by a River: A city sited on or near to fresh water gains health points from the river spaces its citizens work. You can check whether a tile is on fresh water or not by moving the mouse cursor over it.
§ Improve Food Resources: Various food resources - Deer, Bananas and Crabs, to name three - provide positive health points once your workers build the appropriate Improvement on them. And if the improved resource is connected to more than one city by your road, river, and ocean trade network, all of your cities will gain the health bonus. Note that you can never get more than one health bonus from a single kind of resource; if you have two or more of the same resource, you still get only one health point (so you might as well trade the excess resources to your neighbors in return for his or her excess resources).
§ Construct Buildings and Wonders: Some buildings and wonders provide positive health points. The early Aqueduct provides positive health points, as does the Granary.
§ Research Healthy Technologies: Research the technologies which allow you to construct the healthy buildings. For instance you need to know both Mathematics and Masonry to build an Aqueduct. There are a few late-game technologies that also add health to all of your cities.
§ Build Near Woodlands: Cities receive extra health from having Forest tiles in their city radius. Chopping down these forests will reduce the health of the city - be careful not to send the city into starvation!
§ Change Civics: Certain civics add additional health to your cities. Environmentalism is one such example.
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