Natal astrology asks whether a person will travel. Electional astrology, the older branch the Greek sources call katarchic, asks when to leave, and it is in the electional literature that travel gets its most detailed handling.
Dorotheus of Sidon devotes the fifth book of the Carmen Astrologicum to inceptions, the charts of beginnings, and journeys are among its recurring subjects. The technique is consistent across the tradition that follows him. Set the chart for the moment of departure, put the significators of the journey in good condition, and above all watch the Moon, which is the fastest of the seven and therefore fixes the character of a short interval most exactly. A Moon applying to a benefic, in a sign that suits the kind of travel, and out of the way of Mars and Saturn, is the basic requirement.
Two further rules recur often enough to name. The ascendant and its lord stand for the traveller, so they are kept clear of affliction. The fourth house, being the end of the matter, is watched for what the journey will come to rather than how it will start.
Election makes the strongest practical claim of any branch of astrology and is the branch modern practice uses least. It is described here because it is where the tradition's material on ordinary activities actually lives. A natal chart says what a life contains. An electional chart is where astrologers wrote down what they thought a good moment looked like.