Are halachic times for prayer, comencing Shabbos, ect. calculated according to a persons exact location or is there one "time-zone" for the entire city?
And if yes, how would this apply for large cities such as New York City or Yerushalayim (may it be rebuilt), could each neighborhood count as its own city? From where in the city is the zmanim determined; Maybe the center, or the synogogue or the earliest point? Sources and explanations apreciated.
NB: as a fun bonus question, if the time is determined by the exact location what do we do when a person is half in and half out of shabbos? (This happens very breifly twice every week.) Does it follow rosho-v'rubo? Is it chatzi shiur assur min hatorah? I know this is entirely not practical, but I take a que from the Chazon Ish in his קונטרס יח שעות on the halachic international dateline.
שעיקרי ההלכות הם עצילות, ורק אחר צמצום אחר צמצום הם משתמשים בעולם העשיה.
Related: Precise Zemanim?