Young adults represent the future of New Zealand's economy, so I think it's interesting to look at what is happening to them over time.
Using Census data I've made some dotmaps of population changes between 2013 and 2001. In the following maps, there is one blue dot for each new person in census area units that experienced population growth over this time, and one red dot for each person lost in areas where the population shrank.
In each case the maps compare changes in the total "census usually resident" population with that of young adults aged 20 to 34. People in this age group are generally finishing up education, entering the workforce, starting families, and buying houses. The maps show changes in where people live, which reflects a number of factors including earning prospects and cost of living (among other things).
First, the national picture. Total population increased in all of the major cities, most smaller centres, and many rural areas too. In comparison the increase in young population is more concentrated on urban centres.
In the Auckland region, total population increased in almost all areas. The changes in young adult population are very different - a big increase in the CBD but reductions in many areas surrounding the CBD, and growth in outlying areas. I would hypothesise that this reflects housing costs more than anything.
The areas just to the west of the CBD (Freeman's Bay, Ponsonby, etc) are especially interesting. The total population in these areas grew very little between 2001 and 2013, while the young adult population reduced significantly.
I'd like to turn the data behind these pictures into an interactive map and include other age groups also. If anyone would like to help with that or wants the data, let me know.