Modern Western astrology uses a vast array of different house division systems, each one with their passionate adherents. In fact, one author wrote in a book on astrology that if you want to start a fist fight amongst astrologers, just ask them which house system is best!
Signs are different from houses. The signs of the zodiac constitute a celestial frame of reference for the heavenly positions of planets as they move along the ecliptic, or the orbital path they take, at varying speeds, from a little under a month to go through the whole zodiac for the Moon, to around 248 years to make the same trip for Pluto. The twelve houses constitute a mundane frame of reference for the planetary positions, or where their positions were in relation to the earth at the moment of birth. Rising on the eastern horizon is conjunct the Ascendant, or first house cusp; culminating in Midheaven is conjunct the tenth house cusp; setting on the western horizon is conjunct the seventh house cusp; and so on... Although the different planets have vastly different orbital speeds or periods through the celestial zodiac, due to the daily rotation of the Earth on its axis, each planet makes the trip through all twelve houses in the course of a 24 hour day.
Most systems of house division used today are called quadrant based. In these systems, the Ascendant, or eastern horizon point, constitutes the cusp of the First House, the Nadir the cusp of the Fourth House, the Descendant the cusp of the Seventh House, and the Midheaven the cusp of the Tenth House. The houses progress counterclockwise in their numbered sequence, even though the apparent and visible mundane movements of the planets progress backwards through this cycle of cardinal angles. The various quadrant based house systems differ as to where they place the intervening house cusps, or how they slice up the pie of the horoscope.
In quadrant based house division systems, the houses are NOT all of equal width in terms of degrees, but in the Equal House System, each house is exactly thirty degrees, or one twelfth of the circle. The house cusps are set by the sign and degree on the Ascendant, which is the cusp of the First House, with the subsequent house cusps set at the same precise degree of each subsequent sign. In this system, the cardinal angles of the Ascendant and Descendant fall exactly on the cusps of the first and seventh houses, respectively, but due to various geographical and mundane factors, the house placements of the Midheaven and Nadir can vary from their usual placement in the tenth and fourth houses, respectively, and can fall into either the previous or the subsequent house to these two. The Equal House system is used by Lois Rodden, and her astrological databank of the natal horoscopes of famous people, and many other astrologers now use it.
I myself prefer the Porphyry system, which is the simplest quadrant based system of house division, simply subdividing each quadrant of the horoscope into three equal parts; it is the oldest quadrant based system of house division, and dates back to the Roman philosopher Porphyry. In classical Greek or Hellenistic Astrology, they used a Whole Sign system of house division, in which the whole sign that the Ascendant falls in constitutes the first house; the next whole sign the second house, and so on. Indian Vedic Astrology also uses whole sign houses, although the whole signs they use are of the sidereal zodiac, and not the tropical zodiac. I also like Whole Sign Houses, because each house is homogenous or uniform in its sign-related qualities and attributes, and there is a one to one correspondence between the signs and the houses. You don't have houses consisting of two, or even three different signs, and you don't have intercepted signs, no matter how high or polar the latitude of the birthplace.
Perhaps the most commonly used house system in modern astrology is the Placidus system, which is medieval in origin. Dane Rudhyar preferred the Campanus system of house division for his Person Centered Astrology. Many modern astrologers like the Koch system (no relation to the infamous Koch brothers!) because it is more earth based. I prefer Porphyry and Whole Sign Houses.
Choosing a house system is a matter of personal experience and preference; you try one on and use it, or you try several on and use them, comparing your results, and finally decide which one you like best. Although there are some modern astrologers who can get very rigid and dogmatic, saying that there is only one true and correct system of house division, I am not one of these, and don't encourage anyone else to be. So, the answer to your question is that there is no single "correct" system of house division - it's a matter of personal experience and preference, and which one rings truest to you, and which gives you the best results - in other words, what works for you. Try on the various house systems that I have mentioned here for the current Grand Cross, and see which system rings truest in reflecting back to you your actual life experience with this Grand Cross, and adopt it as the system you will use. I hope that this helps.
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