It doesnn't exist anymore. In CtP2, all the resources in the city's radius are automatically collected. As the city gets bigger, the city radius expansd though, so its not completely pointless.
The efficiency at which you use the resources collected depends on how many citizens you have (1 citizen gets you 1/8 of the total in the first radius, 2 citizens gets you 1/4 etc.) and how many specialists you have. eg. If you have 3 citizens, and make one a farmer, you gather the resources as if you had just 2 citizens, + 20 food from the farmer.