Assess the terrain to determine techum Shabbat precisely - using a professional surveyor. If he makes a mistake, we correct the error to have the most expanded techum Shabbat - a lenient position. Note that even non-Jewish servants are eligible to testify as to the location of techum Shabbat. Also: A private city becomes a public city - you can establish an eruv for the entire town. But if a public city was adjusted to be private, you still can't make one large eruv for the whole city. There needs to be a small area outside of eruv. Plus a story at the home of the Resh Galuta, establishing the case of a private estate. Also: a discussion of how to divide up a public city, to avoid the public thoroughfare, and establish eruvin on the different sides of the city. Plus, the role of the public thoroughfare.