978. Improperly Designating a Shabbos Base

Eiruvin 7:5

If a person wants to make a faraway spot his Shabbos base but he does not specify the exact location, he has not properly designated a base. Therefore, if a person was on a journey and he stated his intention to spend Shabbos “in such and such place," "in such and such field," "in such and such valley" or "1,000 cubits from my current location" or "2,000 cubits from my current location," he has not established that spot as his Shabbos base. Rather, he may only proceed 2,000 cubits in each direction from the place he is standing at nightfall.

Eiruvin 7:6

If a person states his intention to spend Shabbos under a certain tree or a certain rock, then if there are eight cubits (about 12’) or more under that tree or rock, he has not established it as his Shabbos base because his specifications were too inexact. This is because he could spend Shabbos in four cubits with the other four cubits having been designated his Shabbos base.