Today's astrologers have the ability to select from a wide variety of house systems to use in the horoscope. There are over a dozen different house systems in use today and astrologers have their own preferences. Among the house systems are Equal, Placidus, Koch, Regiomontanus, Porphyry, Campanus, Morinus, Topocentric, Solar and more.
Houses of the horoscope are derived from dividing space, time or the ecliptic. When you read Sun Sign columns in magazines and newspapers or when the birth time is completely unknown, the system employed is the Solar House system. In this technique the Ascendant is formed by placing the Sun of the individual on the Ascendant.
The system that continues to be the most popular in use today is Placidus which originated in the 17th Century. It uses the four angles of the horoscope formed by the First, Fourth, Seventh and Tenth houses. (Mc/Ic axis and Ascendant and Descendant.) It does not, however, do well when working with latitudes that are in the far northern regions, as the houses will squeeze the other houses around them which creates what astrologers call 'interceptions.'
The Equal House system is also used extensively. This system will take the degree of the Ascendant in its sign and assign each subsequent house the same degree with the following Zodiac Sign. There are no squeezed houses in this system as all signs are represented with an equally spaced house.