Most metrics made in a model are only available in that model. These can be called local metrics. However, there are also some global metrics available in all Guesstimate models, and other organizational metrics available to organizational models.
Guesstimate maintains a database of certain global metrics that can be used in any function in any model. Right now, this dataset is limited to city population sizes, for a select, but extensive list of cities. To use these metrics, simply type an '@' sign, followed by the city name, then a '.' followed by the word, 'population' within a functional form, like this: