95:3 Only a city has a karpeif. A single house doesn’t have a karpeif. In the case of a lone house, the Shabbos boundary is measured from the wall of the house outward. (The minimum to be considered a city is three courtyards, each with at least two permanent houses – OC 398:10.)
95:4 If two cities are near each other, each has its own karpeif. Therefore, if there isn’t more than the width of two karpeifs between the cities, they are treated as a single city.