It's spring, the property market is running hot and familiar debates are raging. Have prices overshot? Is there a bubble? Will investors get burned? How can we help first home buyers? But as the state of the property market is canvassed daily, there's surprisingly little discussion about how the dynamics of that market affect how we live, and the way our cities function.

Over the past two decades patterns of housing affordability in Sydney and Melbourne have shifted as the values of properties close to the city grew much faster than those in outer-ring suburbs. This became entrenched during the great property boom from 1997 to 2003. With each subsequent run-up in house prices. the inner-city price premium seems to grow.

Illustration: Kerrie Leishman.

It's taken for granted these days that houses close to the central business district cost much more than those in outer suburbs - but it wasn't always so. In 1990 the median house price in the Sydney suburb of Lewisham, six kilometres from the Sydney GPO, was similar to North Parramatta, which is 21 kilometres west. The median in Melbourne's Albert Park, four kilometres from Melbourne's CBD, was just a little higher than Box Hill, which is 15 kilometres east. Across both cities, the price differential between the most expensive postcodes and the least expensive was relatively small compared with now.

The upshot after decades of house price growth favouring the inner-ring? Lewisham's median price is now 57 per cent higher than North Parramatta's and Albert Park's median is 50 per cent higher than Box Hill's.