The seventh house is a pivot, angular, and its Hellenistic name is Dysis, the Setting. Counting by whole signs it stands in opposition to the rising sign, the strongest configuration to the Horoskopos there is.
It has a distinction none of the other eleven houses can claim. Every house system in ordinary use places the seventh cusp at exactly 180 degrees from the ascendant. The quadrant systems do so because the descendant is by definition the opposite point of the ecliptic; Equal does so by construction; and whole-sign does so in effect, because the seventh sign from the rising sign is necessarily the sign holding the descendant degree. Where the systems can put the second, third, fifth, sixth, eighth, ninth, eleventh and twelfth cusps many degrees apart, and can disagree about the fourth and tenth in whole-sign and equal, the descendant is fixed.
That makes the seventh the one house whose contents are the same under every system except for the whole-sign boundary effect, which is the ordinary difference between a sign-based and a degree-based scheme.
The consequence for practice is worth stating positively rather than as a caveat. A reading of partnership and open opposition, which is what this house carries, is the reading least likely to change when a chart is recast in another system, and it is therefore among the safer things to say about a chart of uncertain provenance.