משנה אויף במדבר 35:5

If he does not recognize [any tree or fence], or if he is not familiar with the halakhah, and said, “Let my present position be my Shabbat place”, his position acquires for him the right of movement two thousand cubits in any direction. In a circle, the words of Rabbi Hanina ben Antigonus. But the sages say: the distances are square, in the shape of a square tablet, so that he may gain the area of the corners.

On that day Rabbi Akiva expounded, “You shall measure off two thousand cubits outside the town on the east side” (Numbers 35:5). But another verse states, “from the wall of the city outward a thousand cubits around” (vs. It is impossible to say that it was a thousand cubits since it has been already stated two thousand cubits; and it is impossible to say that it was two thousand cubits since it has been already stated a thousand cubits! How then is this so? A thousand cubits for the field [surrounding the city] and two thousand cubits for the Sabbath-limits. Rabbi Eliezer the son of Rabbi Yose the Galilean says: a thousand cubits for the field [surrounding the city] and two thousand cubits for fields and vineyards.

One who vows abstinence from a bed is permitted a couch, the words of Rabbi Meir. But the Sages say: A couch is included in “bed”. If he vows abstinence from a couch, he is permitted the use of a bed. One who vows not to benefit from a town, may enter the town’s [Shabbat] border but may not enter its outskirts. But one who vows not to benefit from a house, is forbidden [only] from the door-stop and inwards.