Deuteronomy 3:10 (ESV)

10 all the cities of the tableland and all Gilead and all Bashan, as far as Salecah and Edrei, cities of the kingdom of Og in Bashan.

The kingdom of Og is described here in terms of a threefold division, where the tableland is the southernmost section, Gilead the next stage, and Bashan the northernmost area.