There are two uses of the word "resources" that can lead to some understandable confusion.
First, there are the 23 tiles within the fat-cross of your cities that can produce hammers, commerce or food when citizens are assigned to work them.
On the other hand, there are health, happiness and strategic resources that are located within your cultural borders, regardless of whether or not they fall within the fat-cross of any of your cities. These need only to be improved (mine, farm, plantation or camp) and be connected to your cities (road or river). These resources allow you to grow your cities larger
) and
) or build certain units or certain buildings faster.
First, there are the 23 tiles within the fat-cross of your cities that can produce hammers, commerce or food when citizens are assigned to work them.
On the other hand, there are health, happiness and strategic resources that are located within your cultural borders, regardless of whether or not they fall within the fat-cross of any of your cities. These need only to be improved (mine, farm, plantation or camp) and be connected to your cities (road or river). These resources allow you to grow your cities larger

