Hello

This information is required to avoid off grid errors. Foundries can typically snap their mask dimensions to a certain scale. This will be part of the DRC rule manual and also you should find it in the rule deck.

You can always check it in your techfile by running a SKILL command in CIW:

Code:

techGetMfgGridResolution(techGetTechFile(geGetEditCellView())) 

(basically what it does is call the techfile and render the info for you if I understood correctly myself)
it should output a value in um