(added on 2008/11/07)
Transmission of a phenomenon 一個現象的傳播
Some heroin users have a tendency to become addicted to more than one drug. The map shows the evolving pattern of this multi-drug taking phenomenon over a 20-year period from 1986 to 2005. The habit began from a small focus in urban Kowloon which subsequently spread to other parts of the entire territory. Unlike infection the habit spreads through peer influence rather than a microorganism.