I have been manually adding houses by drawing them by hand using JOSM. It is a big job.

FYI I just used osm-revert to do a partial revert of this changeset, adding back the development at Gloucester Green and Madras Square. I manually recreated the deleted developments near the town hall and Manchester Square.

Nah no worries mate I added them back.

Yes, the LINZ datasets are a year or so out of date.

A lot of buildings have gone up in the meantime and I've been manually adding them where I can. Rather than wait for aerial imagery to be updated, I look for any site plans submitted for council consent so I can get accurate building footprints. This means in some cases the buildings are on the map before the LINZ imagery shows that they're there.

If the aerial imagery shows an empty lot, but a building is present in the map data, I would check the changeset history for the object to see when it was last updated. If the building was added very recently then I leave it alone, but if the building was added to the map a long time ago then it has probably been recently demolished, and can be removed. I think that is the best way to check.

Generally speaking we're past an inflection point in the city rebuild. That is to say, most of the demolition has already happened some time ago, and there are relatively few recent demolitions. However there are lot of new builds going up right now, so it is always good to double check before deleting something.

The LINZ building outline data (https://data.linz.govt.nz/layer/101290-nz-building-outlines/) is pretty good, but it is built from computer-vision processing of the latest aerial imagery, which means it is just as out-of-date as the most recent aerial imagery (currently that is Nov 2023). This is why it can be risky to just bulk import data from other sources, even LINZ. I learned this the hard way when I did a bulk import of bus stops a few years ago from the Metro API and clobbered a bunch of work others had done on them by hand.

In general, its best to rely on multiple sources rather than just aerial imagery or LINZ data alone.

Happy mapping!

FYI this deleted a number of new buildings I had manually added from physically visiting location, for example the Quest on Kilmore hotel