No public transport system can efficiently cope with low density. All the good systems in the world belong to dense cities; and none of the sparse cities has a good system. Public transport in large areas of low demand will always be structurally inefficient: services are infrequent, unconnected and far apart. Anyone who has waited a long time for a bus or tram or train always says the same thing: ''They ought to put on more services.'' But the operators can only put on as many services as there are enough passengers; and the sparser the population, the fewer the services, the higher the levels of frustration and the greater the incentive to use cars. The same argument occurs with the route. Alas, the volume of patrons needed to justify a geographic proliferation of services is only produced with greater density. Last year public transport analyst Paul Mees released figures on various other wasteful cities and saw no correlation between urban density and efficiency. But his data set turns a blind eye to the extreme contrast between low and high density. If we compared all of the low-density cities (with whatever variation) with all of the high-density cities (such as Singapore, Seoul, Vienna and Paris), the results would be more meaningful. Australia has the luxury of space, but it also suffers from the grind of distance. The spacious and leafy suburbs have aesthetic appeal; but the problem is that we have to move around them, enormous distances at a time, for shopping, day care, doctor, school or work. We're so spread out that the probability of services lying close to home is slight. None of this would be so bad if everyone went around on bikes; but the distances require cars.

Some greenies believe that suburban gardens can be justified if we grow vegetables in them rather than ornamental trees; but from a greenhouse point of view, the consequences are similar. Horticulture in the city is in the wrong place. Some gardens yield pleasure for their custodians, but other gardens are forced on us by convention. They're imposed by mandatory gardening legislation, which is called ''setback'', a body of local regulation that disallows building over gardens even if the owner doesn't want a garden. A huge amount of land lies at the border of dwellings that is good for nothing but is protected under the law. A typical case is the strip that runs around blocks of flats. Such spaces can be called negative gardens - these have no presence by themselves but are instituted solely for the purpose of backing away from the street or in compliance with setback laws. The beautiful towns in Europe - such as Paris and Vienna - show that these ugly gullies between buildings, in front and to the side, are totally unnecessary. And whereas European architecture has legendary presence, our places, surrounded by negative gardens, look weak and equivocal, as if neither garden nor house has a rationale to be where it is. Setback regulations systematically prevent efficient development. Because we can't use the whole block, we tend to add to the shell of an existing house, which means that the project merely produces a more wasteful household for one family rather than a taller, wider building for five or 10 families. The McMansions that sit within their setback all have to be heated and cooled, with calamitous per capita environmental cost. The only way we can ethically justify this wasteful ecological damage is to invoke heritage values and deplore the living conditions in other parts of the world. And, yes, heritage is important. But we can't ethically protect it forever against the survival of the biosphere.

There's no point protecting our street with vigilante pride if the whole planet is doomed by global warming. Besides, a pretty, low-rise street in one zone means a throttled highway only metres away; and ultimately, what we're protecting is an urban mess. As an aesthetic historian, I'm the first to concede the value of heritage. But some aspects of heritage deserve to be disowned. Most of inner Melbourne is unfit for the purpose of a town of 3.6 million people. Our heritage is largely dysfunctional. When Australians face a challenge to suburban orthodoxy, they often try to portray it as an expression of inner-city contempt for the outer suburbs. From an ecological planning point of view, however, urban density is just as important in Ringwood and Dandenong as it is in Carlton. It's as important to be close to services in St Albans as it is in Kew. The debate isn't about inner versus outer. Our aesthetic and moral agenda must be to increase density throughout our sprawling city. Robert Nelson is associate dean at Monash Art & Design and Age art critic.