Exterior Walls and Omed Merube in Crown Heights
The proposed outer boundary is described as being made mostly from existing walls. In halacha, omed merube al haparutz can allow a wall with openings to remain a wall. The calculation applies only after the actual sides, walls, openings, and breaches of the enclosure have been identified.
The calculation begins with a defined enclosure
Omed is standing wall and parutz is open space. Their proportion is not ordinarily taken as one undifferentiated total around an entire city. The relevant wall or side must first be defined, and openings with an independent disqualifying status must be treated before the remaining lengths are added.
A percentage therefore needs a denominator: the exact perimeter or side being measured. It also needs an accounting method: which structures are included, how corners and offsets are joined, how the width of each opening is measured, and whether a roadway or other breach can be counted merely as part of the open percentage.
The only published figure for this route is 80 percent walls. The underlying wall lengths and open lengths have not been published with the map.
Which structures can be counted
A building wall must be high enough and continuous where it is being counted. A fence must be assessed at its gates and damaged sections. A retaining wall or railway cut depends on the height and steepness of the drop. An embankment that rises gradually is not the same as a vertical mechitza. A highway barrier built for traffic may be interrupted at ramps and crossings.
The side of the structure facing the enclosed area matters as well. The principle of gud asik or gud achis cannot be invoked from a diagram without establishing the edge from which the halachic wall is said to rise or descend and whether people pass through it.
Where the walls lie miles from Crown Heights, the intervening streets, bridges, railway openings, parks, and neighborhoods remain inside the claimed enclosure. The system must close that complete outer route; distance does not allow separate pieces to be treated as though they touch.
Openings and interruptions
An ordinary opening may sometimes be closed with a valid tzuras hapesach. Larger breaches and public streets raise separate rules. A breach wider than ten amos is not simply another few feet in the citywide percentage, and a public opening sixteen amos wide cannot be dismissed by saying that most of the distant perimeter is walled.
Bridges and tunnels are especially important because they allow streets to pass through natural or man-made boundaries. A water edge, rail cut, or highway wall may appear continuous on a map while the traffic route through it remains open. The wall on each side of that crossing and the halachic treatment over the crossing have to meet.
The Crown Heights ruling
Rabbi Osdoba and Rabbi Braun addressed the publicity concerning purported mechitzos outside Crown Heights. They did not accept the expanded perimeter as a new basis for carrying. Their words were that there was “no change whatsoever” in the categorical rejection already issued by the local Rabbonim.
The current practical halacha therefore does not turn on whether the public sees an 80 percent figure, a revised map, or a weekly status notice. The Crown Heights Beis Din has ruled that the outer-wall proposal does not permit carrying in the neighborhood.