Madinah, known before Islam as Yathrib, is an ancient city surrounded by volcanic rock and blessed with abundant groundwater, which allowed extensive date palm cultivation: along with Khaybar, one of only two places in the Hijaz with such large groves. The Prophet ﷺ renamed the city Madinah ('The City') and also called it Tabah and Taybah ('the Pure'); the name Yathrib, which some scholars trace to words meaning 'to criticize' or 'corruption,' appears in the Qur'an only on the tongues of the munafiqun.
Madinah was reasonably close to Makkah (roughly 7-8 days by caravan, about 3 by fast rider) without being too close, and was naturally defensible: volcanic lava plains protected its east and west, and dense date-palm cultivation protected its south, leaving only the north exposed -- later fortified with a trench at the Battle of Khandaq. Its people, the Aws and Khazraj, had never been conquered and had a strong, independent spirit; both were Qahtani Yemenite tribes, unlike the surrounding Adnani tribes, so their union with the Muhajirun crossed old tribal and ethnic lines. Having lived alongside the Jewish tribes of Yathrib for two centuries, the Aws and Khazraj were already familiar with the concept of revealed books, prophets, and shari'ah, which prepared them to accept Islam readily.