Houses divide the sky into twelve areas of life. Whole Sign houses simply give one full sign to each house, starting with the rising sign. Placidus divides the sky by time — by how long each degree takes to rise — so houses can be of unequal size.
Whole Sign is ancient, clear and robust when a birth time is uncertain. Placidus is sensitive to the exact minute and to latitude, which makes it expressive for precise charts and awkward far north, where some signs rise very quickly.
For Riga and similar latitudes, Placidus houses can stretch noticeably. A planet may sit in a different house under each system, and an honest reading mentions that rather than hiding it.
This atelier uses Placidus for its precision with verified birth times. The point is not that one system is true and the other false; it is to choose a method deliberately and apply it consistently.
Other systems exist too: Koch, Porphyry, Equal, Regiomontanus, Campanus. Each answers the same geometric question — how to divide a sphere into twelve sectors from a point on Earth — with different assumptions. None is a mistake; they emphasise different things.
In Whole Sign houses the Ascendant degree remains important but floats inside the first house rather than defining its start. The Midheaven may fall in the ninth, tenth or eleventh house. Practitioners of this system read the Midheaven as a point, not a house cusp.
In Placidus the Midheaven always marks the tenth-house cusp, which is why it feels natural to many modern astrologers. The cost is unequal houses, and at high latitudes a sign can be intercepted — wholly contained within one house without appearing on any cusp.
A practical test is to read a well-known life with both systems. Notice which placements explain the visible story more clearly, and which feel forced. Over time most astrologers form a reasoned preference rather than an inherited one.
When a birth time is only approximate, Whole Sign gives a steadier frame because a small error rarely changes the rising sign. When the time is recorded to the minute, Placidus can reveal finer distinctions, especially near house cusps.
Clarity with clients matters more than the system itself. If a planet sits close to a cusp or changes house between systems, say so and read both possibilities instead of pretending the boundary is sharp.
Consistency is the final rule. Changing systems from chart to chart to find a nicer answer is not technique; it is wishful thinking.