As we have seen (section 2), we square a person’s mekom shevita to determine his teĥum. If he is in a field (i.e., not in a city or town), his mekom shevita is a square with four-ama sides; if he is in a city, we inscribe the city in a square. From this square we measure 2,000 amot in each direction.
Let us add now that when we square the city, we do so based on the four cardinal directions (SA 398:3). If the city already has corners that lend themselves to squaring in a way that does not follow the four cardinal directions, the squaring is done accordingly (SA 398:1).
Examples of squaring based on the four cardinal directions:
Examples in which it is agreed that the squaring does not follow the four cardinal directions:
When a city’s shape lends itself to squaring that does not correspond to the four cardinal directions, the poskim disagree how to square it. Some maintain that only when there is a compelling reason not to follow the four cardinal directions may one follow the layout of the city (SAH 398:3; Ĥayei Adam 76:14). However, most poskim maintain that if the shape of a city clearly lends itself to squaring in a certain way, we follow this squaring even though it does not correspond to the four cardinal directions (see n. 7). In cases of doubt, the local rabbinate or rabbinic authority should make the decision.
Examples of such intermediate cases in which a city’s shape clearly lends itself to squaring in a direction other than the four cardinal directions include cases where one side of the city is straight from one end of the city to the other (figure 1) and cases where the perimeter of the city contains a right angle (figure 2, in which case we follow the directions of the right angle and not the four cardinal directions).
It is important to note that if one is spending Shabbat outside a city and his mekom shevita is limited to four amot square, he may choose to square his mekom shevita in whatever direction he wishes, and this will also determine how his 2,000-ama teĥum is squared (see section 12 below).