Charting the Andromeda Galaxy for habitable planets presents a unique challenge. Observation is limited by light, and given Andromeda's distance, any observations from the Milky Way are 2.5 million years out of date—enough time for a planet to have altered irrevocably.
Initial attempts to identify settlement sites were made by obtaining asari astronomical surveys and running them through predictive models. But Jien Garson was unwilling to risk thousands of colonists without solid information.
Eventually, the Initiative obtained promising data from quarian explorers who claimed to have found a geth array on the fringes of the Perseus Veil. This array was supposedly built from three mass relays, using sensors in the combined relay corridor as a form of FTL "telescope," to observe dark space beyond the galactic rim. Why the geth expended so much effort to study dark space is not known.
Amongst these observations were near-contemporary surveys of Andromeda. When our predictive models confirmed them within an acceptable margin, the Initiative was able to begin identifying "golden worlds."