Karpaf part 1 – Eruvin 23b
(excerpted from The Contemporary Eruv)
An area is considered eino mukaf l'dira [not enclosed for the purpose of habitation] if it is not an area designated for human habitation. We call such an area a karpaf. If a karpaf that is larger than five thousand square amos (a “beis se'asayim”) is included within an eruv it renders the entire eruv invalid (Shulchan Aruch, 358:9; see also Hilchos Eruvin 7:3-15; Yesodei Yeshurun, ibid., pp. 261-265; She'arim Metzuyanim B'Halacha 83:4-6 and the Kuntres Acharon there; Tzitz Eliezer 13:41; and Nesivos Shabbos 12-13).
The Poskim extend the definition of human habitation to include any use of the area in question for human needs. This would include parks and any other area suitable for walking or strolling, but not planted fields, unless there are walking paths between the furrows. Rabbi Akiva Yosef Kaplan noted that in the source of this Halacha, the Chacham Tzvi, siman 59, cited by the Sha’arei Teshuva, Orach Chaim, 358:8, it seems that it is not necessary that a pathway exist between the furrows, but rather only that it be possible to walk between the furrows. Rabbi Kaplan continued to posit that it seems sensible to assume that there must be a requirement of paths. Otherwise, there practically always exists at least some possibility of walking between the planted rows! Perhaps we might contemplate a “compromise” position: If a pathway exists, that certainly is sufficient. If no path exists, but permission can be secured from the owner of the property to walk at regular intervals through his field in ways that would diminish the “impassable” planted area to an area of less than beis se’asayim, that may nullify the karpaf problem as well. (More extensive discussions concerning the necessity and width of the path are to be found in Kesser Ephraim, siman 43; Hilchos Eruvin and note 165 there.)