Eiruvin 55a, b

We are told how to measure the edge of a city.  If the city is round, we create a square around the edge of the circle and then measure 2000 cubits distance to create a larger square area around the city.  If the city is strangely shaped, we use the outlying structures - including a cave, church, grave, etc. as long as it has a roof and a residence in it - to create a square around the city.  Again, the 2000 cubits are measured around that square.  

The Gemara goes into some detail regarding a city in the shape of a bow.  It tells us that we imagine a line that runs from one end of the city to the other.  To create a Shabbat limit in such a city, one will be allowed to walk from the centre of that line toward the city.  Even if the distance is longer than 2000 cubits, one should be able to use those boundaries.  The rabbis debate about whether or not we should take into consideration the length from one end of the town to another.  They create interesting measurements to further elucidate their points. As well, they speak of a 'karpef', an area of seventy cubits that can be added to the area of any city, and its relationship with the 2000 cubit measurement.

The rabbis have an interesting conversation about people who live in huts.  they argue about  whether or not a group of huts or tents should be called a city, thus requiring Shabbat limits.  Rabbis argue about the Israelites in the desert living in huts.  Surely they were in cities requiring Shabbat limits, and certainly Moses creating that eruv!  Rabbis assert that those who live in huts are reprehensible - they do not have access to water and one should not marry their daughters.  One of the reasons put forward for this stringency is that these women are adulteresses when their husbands are gone, and thus we do not know who are the fathers of their babies.  This is important, of course, because of questions of lineage which were so important to the maintenance of the social structure of the time.  

The harshness lashed upon those who live in huts - shepherds, very poor people - goes against much of what the rabbis teach in other circumstances.  Are we not supposed to be generous with strangers, for we were once strangers in a strange land?  Culturally created (as opposed to Torah-created) oppression becomes easier to sift out when running fingers through the sand every day.