by Maurice Fernandez
The dilemma of house system use is part of the astrology study process. Many students usually follow the system used by their mentors, though greater research can be useful to really determine a choice of one’s own. Perhaps, the use of more than one house systems would be the most sensible approach as each House System highlights different things in the chart.
It is crucial to remember that ALL house systems have their valid references and logic. Astrology is a blend of Astronomy/Nature references with Symbolism references, so approaches vary. Some systems will refer more heavily on astronomical coordinates, while others will rely more heavily on the symbolism references.
Location based House Systems where the Ascendant/Descendant and MC/IC natural intersections between the earth and the sky are serving as the indicators of the chart angles: Houses 1- 4 – 7 - 10
The inner houses (2nd, 3rd, 5th, 6th, 8th, 9th, 11th, 12th ) will vary in each of these systems:
Placidus – Most widely used by Western Astrologers. Once the location based Ascendant and MC Axes are determined, the system uses a time based reference to divide the inner houses. The paths drawn for each degree of the ecliptic to move from the nadir to the horizon, and from the horizon to the midheaven, are trisected to determine the cusps of houses 2, 3, 11, and 12.
Koch – The Koch house system refers to the Midheaven at the time of birth. The time is then turned back - to put it simple - until the zodiac degree, which formed the Midheaven in the chart, is made Ascendant. This temporal distance is trisected, and in this way the cusps of  and  are obtained from the respective Ascendants (see figure on the left.) The cusps of  and  are formed in a similar way using the distance to the IC. To put it differently: The cusp of  is the point on the ecliptic that has been above the horizon for one third of the time that the Midheaven degree has been above the horizon. Similarly, the cusp of  has been above the horizon for two-thirds of that time (from Wikipedia)
Porphyry – Here, the space between the Ascendant and MC angles is divided into three equal parts.
Regiomontanus – Commonly used by Horary Astrologers, with reference to the work of William Lilly.
In the Arctic Circle, beyond the 66 North Latitude, the Locational House Systems will not be used because the MC collapses on the Ascendant. Only Zodiac Sign based house systems (See below) are possible from that latitude North.
Which house system to use if planets change houses: All house systems have their valid references. Perhaps a way to reconcile between the different ASC/MC house systems is to refer to a planet as influential in both houses if it switches positions from system to system.
Zodiac Sign based House Systems where houses are aligned in greater precision with the 30 degrees size of signs.
Equal House – The Ascendant degree opens the 1st House, and the rest of the houses are divided equally into 30 degree parts.
Whole House – The Ascendant sign is used to determine the 1st house, but every house will open at the zero degree of each sign to preserve a symmetry between houses and signs.
Solar House – The degree of the Sun is the degree of the Ascendant, and the rest of the houses are divided equally into 30 degrees from that reference. This system is usually used when no birth time is available.