Complex sentence: Ley's book' The New Middle Class and the Remaking of the Central City'was central, in which he describes patterns of urban gentrification in six Canadian cities and outlines a demand side explanation to gentrification, as oppose to Smith's supply side explanation.
Split into simpler sentences: Ley's book "The New Middle Class and the Remaking of the Central City" was pivotal, in which he describes patterns of urban gentrification in six Canadian cities. The book outlines a demand side explanation to gentrification, as opposed to Smith's supply side explanation.