Watch the Ham's Rag online guitar lesson by David Hamburger from New School Fingerstyle
Ragtime as created by pianist/composer Scott Joplin and other turn-of-the-20th-century musicians was thoroughly composed, included numerous sections and frequent key changes, and was played with a straight eighth note feel. The alternating thumb of ragtime guitar imitates the left hand of ragtime and barrelhouse pianists but without as much of the harmonic or formal complexity. "Ham's Rag" is essentially a John Hurt-style ragtime guitar piece that sneaks in a modulation to E minor in the bridge.
Reference Source: John Hurt (http://www.vanguardrecords.com/Hurt/home.html)