Which hook for manipulate distance before Views "sort criteria" is activated?

Hello,
i use a Location View with Distance/Proximity to display nodes "in the near" - it works perfect!

But i have a question!

In my Views-fields i use field "city" (amongst other things)! For results with specials citys i must manipulate the distance BEFORE Views "Sort-criteria" will be active (i sort over Distance/Proximity)!

Example: Result with city "Berlin" and original-distance with 10,98 km (for example) i need distance set to "0 km" (before Distance/Proximity-sort-criteria will be active).

With which hook/function can i made this?

Sorry for my bad english - i hope you understand my problem.

Thanky you very much!

Best Regards Matthias