A method of using climate data to determine activity index values for a given activity. One embodiment provides a method of more objectively determining the desirability of an activity based on climate data by determining an activity index value using a weighted-element type analysis. Multiple activity index values may be determined for different time periods and used to provide information useful in comparing the desirability of the different time periods for a given activity. The activity index values may be used to answer questions such as "what is the best month to visit Kingston, Jamaica" and "what is the worst season for allergies in Atlanta."