The angular houses are houses 1, 4, 7, and 10. These houses represent the basic needs, the foundational parts of life. The cusps of these houses are the angles of your chart– The Ascendant and Midheaven. And their counterparts, the Descendant and Nadir.
Your self, appearance, mannerism, approach
Your partnerships (marriage, business partnerships, or any cooperative venture)
Your career, what you offer the world, the role you play in the public sphere
Your home, family, emotions, roots
The angular houses represent the most fundamental issues in life. A planet in one of these houses has extra strength and power in the chart.
The cusps of the angular houses are called the angles of the horoscope. These cusps are very important in astrology, and have a few different names.
Sign on the Ascendant
Describes people’s first impression of you, your personality. Your identity. Your physical characteristics.
Sign on the Descendant
Describes your partner, what you look for in a partner. Aspects of the self that influence attraction.
Sign on the I.C.
Describes your early emotional environment, family of origin. How you like your home to be. Emotional safety.
Sign on the M.C.
Describes your career, achievements and ambitions, what the world remembers you for.
The first house, representing you, is directly opposite the seventh house, representing your partner. The tenth house, representing public life, is directly opposite the fourth house, private life.
You can picture these pairs like two ends of a see-saw calling for balance and co-operation between the two. Balance in relationships, and work-life balance.
Any planet conjunct (within 10 degrees of) these house cusps, on either side, has a strong influence on that angle and those ideas it symbolizes.
Note: the angles represent the horizon line (the places due east and west of you at the time of your birth) and the meridian line (due south— the highest point on the ecliptic, and due north). These four house cusps will be the same no matter which house system you use. However, for the rest of the house cusps, there are many ideas about how best to place them. Different house systems work well for different astrologers.
My take-away is this: while angular house cusps do have precise locations, the rest of the house cusps seem to be “fuzzy” or less defined. More of a gradient than a well-defined boundary. Therefore, I think you can assume some “wiggle room” with the placement of all house cusps except for the angles.