synastry

Positions come from a compact orbital-mechanics approximation, not a full ephemeris — expect sign placements to be right and degrees to be close, generally within a fraction of a degree for the Sun and within about a degree elsewhere. Houses use the whole-sign system and need a birth place; skip it and you still get full planet-to-planet synastry.

the tightest aspects between you

house overlays — whose planets land where

In synastry, the house a partner's planet falls into is often read as more concrete than an aspect — it says where in your life they show up, not just how.