Artists use samples in a range of ways: some use a sample primarily just for the sound it contributes to the new product, and take such small samples that the source is virtually unidentifiable. But others choose samples for the meaning and associations they bring with them; I decided to "trace" one of these latter samples. "Ain't No Love In the Heart of the City" is a 1974 R&B song by Bobby "Blue" Bland--on the surface it's a love song, but many listeners and artists have interpreted it as a lament about urban poverty and the effects of systemic racism. It's been covered many times, and sampled, including by Real Live and Kanye West for Jay-Z. The Jay-Z song, in turn, has been sampled several times, including by Dave East and Trey Songz, Diamond D, and Italian rapper Bassi Maestro, among others. A quick look at the titles of the songs on the list shows how associations with the original R&B song and the Jay-Z song accumulate and morph over time, inspiring later uses of the samples.
Crowdsourcing
Bring That Beat Back : how sampling built hip-hop by 
Making Beats : the art of sample-based hip-hop by 
Rhymin' and Stealin' : Musical Borrowing in Hip-Hop by 
The Pop Palimpsest : intertextuality in recorded popular music by 
That's the Joint! : the hip-hop studies reader by 
The Cambridge Companion to Hip-Hop by 
Resistenza Rap: Music, Struggle, and (Perhaps) Poetry/How Hip-Hop Changed My Life by 