We run a facebook page, camel city nightlife, where we keep track of all the bar specials and events downtown. First Street and Carlisle's are the only two that get coverage outside of the popular definition of "downtown".
There is no official definition of downtown, well...there are LOTS of definitions and borders, but none thats held above all others. The city has adopted I40 and Hwy 52 has hard borders on the south and east sides, but the northern and western borders are moved as it fits the needs of the project.
Ive seen city program maps that stretch downtown all the way to stratford road. Our cut off is generally hawthorn.