For most of this year, Mills Lane at the back of the Herald building has offered the unmistakable stink of urine and a ledge of ramshackle cardboard beds where some of the city's homeless sleep out.

The ledge is not where you would seriously want to park your head. At night there's more than a few vermin which feast on leftovers from the rubbish bags outside fast food joints. But there is also a warm air outlet.

For a long-time Auckland CBD dweller like myself, the daily trek from my apartment brings home the rising numbers of homeless, even though the Mills Lane crew was moved on this week.

There's long been what we used to term "vagrants" dossed down on benches overnight in Jean Batten Place or in front of the Metropolis where I live. Hopeless cases who stank of booze, resisted all efforts by social agencies to get them housed but generally did not make a nuisance of themselves.

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Those "sleeping out" now are not so easily stereotyped.

This factor was underlined by the Big Sleepout which included Blues players Josh Bekhuis and Joe Edwards, singer Lizzie Marvelly, AUT vice-chancellor Derek McCormack, BNZ boss Anthony Healy, Labour MP Jacinda Ardern and Herald managing editor Shayne Currie.

The aim was to turn a public spotlight on to a growing social issue and raise money to help get people off the streets and into homes.

It's a good aim but also one which is fraught with difficulty as the numbers "sleeping out" are just the public edge of a much bigger problem.

In 2009, Statistics NZ devised a "New Zealand definition of homelessness" as "having no other options to acquire safe and secure housing".

A Government working group sorted homelessness into four categories - those without shelter (living on the street or in cars), those in temporary accommodation (overnight shelters), those sharing accommodation (bunking down on couches in friends' flats), and those living in uninhabitable housing (dilapidated dwellings).

In 2013, a University of Otago study decided the term "homelessness" had burdened the issue by stereotype and substituted the term "severe housing deprivation".

Other groups like the NZ Coalition to end Homelessness have proposed new measures including "wet houses" where those with long-term alcohol dependency can consume alcohol in a safe environment.

As expected, children, young adults, ethnic minorities and sole parent families are among the "severely housing deprived".

Otago University also points to other factors - new migration, high residential mobility, limited education, unemployment, labour force exclusion and unskilled work.

When a lens is applied to the four categories which comprise official homelessness - not just "sleeping out" - there is a strong case for ensuring affordable housing stays at the top of the Government's policy thrust.

Studying homeless populations - even under the Statistics NZ broad measure - presents methodological challenges as living situations change. The definition was developed to help diverse organisations measure how many came into such categories.

But in a city where it is now commonplace for young people to doss down on couches because there is a shortage of well-priced rental accommodation close to work or study, where over-crowding is once again the norm in many suburbs and where skilled people are questioning whether they can ever afford to get ahead in Auckland - it is time to develop comprehensive "real time" statistics to quantify the demand pressure.

The desperate shortage of affordable homes is not going to ease any time soon.

It will be exacerbated by continuing high immigration pressures with some smart foreign investors in New Zealand expecting the country to grow well beyond the 4,598,134 estimate as at 4.30pm yesterday on Statistics NZ's population clock to more than 7million within a relatively short space of time.

The Government and the Auckland Council must face up to this growth and ensure citizens do have access to affordable housing.

In the United States, some cities have criminalised aspects of homelessness by issuing ordinances to prevent citizens sharing food and preventing them from lying down in public. This "tough love" approach to those "sleeping out" in the inner city is unlikely to get many public backers.

Where many US states lead New Zealand is by simply dividing homelessness into those who are "unsheltered" and the rest.

This enables both a short-term approach to get those sleeping out into shelters, and a much stronger focus on the bigger issue which is housing - as is the case in Auckland.