Short answers, pulled from the story.
The Salween River marks the western boundary while the Mekong flows along its eastern edge. Rivers including the Ping, Wang, Yom, and Nan flow southward through these valleys to form the Chao Phraya River in Nakhon Sawan Province.
Lanna emerged in the thirteenth century and lasted until the eighteenth century. Historical records link Northern Thailand to early political entities like Hariphunchai Kingdom which existed during the seventh century.
The National Geographical Committee defined nine provinces for the northern region on the 1st of January 1978. Some definitions now include seventeen provinces when adding four upper-central-region provinces such as Kamphaeng Phet and Tak.
Northern Thailand Region produced combined economic output of 1,266 trillion baht during fiscal year 2018. This figure represents 7.7 percent of Thailand's gross domestic product with Chiang Mai province ranking second in per capita income.
Northern Thai functions as a southwestern Tai language spoken daily by approximately six million people across nine changwat regions. Central Thai serves as the sole official language throughout Thailand while various hill tribe languages exist alongside major Tai dialects.