A more thorough explanation:

Definition: Thence is an adverb that means "from that place" or "from that time." In surveying, it is used to describe land by courses and distances, indicating that the following course is continuous with the one before it. It can also mean "on that account" or "therefore."

• Surveying: We walked south 240 feet to an iron post, thence west 59 feet.
• Time: She left the party at midnight and thence went home.
• Reason: He failed the test, and thence he had to retake the class.

The first example shows how thence is used in surveying to indicate the continuity of courses and distances. The second example illustrates how thence can be used to indicate a point in time. The third example shows how thence can be used to indicate a reason or consequence.