The only 'boundary on the ground' is a fence line to the north. I do not see anything else where.
The present OSM boundary looks to encroach on the residential property to the east according to the LPI base Map. Elsewhere the OSM boundary looks to be arbitrary.

In OSM the 'roof' bit is usually mapped as a separate building. This makes it easy to tag it with roof and layer and it can overlap the main building, as some of them do.

Multipolygon relations outer ways cannot share segments .. so the relation you crated for this is technically wrong. See https://tools.geofabrik.de/osmi/?view=areas&lon=139.56220&lat=-32.58145&zoom=17

Niggle;
Umm there is an increased use of the word 'practice' associated with sport. To the extent that the sport=skiing is now described as for 'practice' with no mention of the actual sport it self.

Agree with the smaller area for the sport/practice (where a sport is played is it not also used for practice?).
Not comfortable with military=danger... should have a better tag... sigh.

Difficult.
While I agree with the pitch really being the 'playing area', the rest is not really military...

Ummm ... Archery ranges have the same issue. And there are a number of shooting/archery ranges that are not military. Really a land use ? landuse=?danger/safety? Don't know. For other sports there is usually a 'run off area' too. Motor race tracks usually have some danger area too.

Why is relation/10707379 a relation? There does not look to be a need for that.

Most buildings have roofs. Most buildings are at layer=0 which is the default layer. By using layer=1 it says the building is above something.

To me this looks like a service station - a simple building for one part ... and then a roof at layer=1 over the forecourt. Why do they need to be combined? And why is it building=roof;yes, I think most buildings have one value??

The areas that have been tagged as landuse=meadow may simply be lawns.

The imagery cannot establish the 'land use here.

Hey hey .. thanks guys.
I have been adding holes on the tree area using Ersi clarity .. will use the gpx trace to realign the Ersi imagery and correct my mapping! Humm might be better off using Bing .. the Ersi correction changes too much form one area to another...

I'll put in cliff lines once I have done that.

This is not a cycling route .. so it is not an 'lcn'.

I have retagged it as a 'rwn' - regional walking network.

The track you have entered looks to go up a vertical face at about node/6177428032.
Looking at Ersi clarity there is a nice level track that I would think a normal walker would be far happier with.
Later on the OSM path goes further inland that shown on Ersi, but i think this is a track realignment by ParksTas to reduce risks of people falling over the cliff.

Dam depth and capacity? The sourced cannot be the LPI Imagery... were these obtained form the website https://www.esc.nsw.gov.au/copyright-notice?

You will note the CC by 3 license is not OSM compatible.

Merged nodes to remove close node vertices.

Also squared up the way/771529041.

I have changed the residential area to reflect the residential area.. not including the roads. The roads are landuse=highway.
Note that natural=wood can overlap land use, natural=wood is a land cover not a land use.

Way: 382797425 is the bit in question that overlaps the residential area. In particular Node: 3860149903 is the node if moved or deleted would remove the overlap. This node was entered on 2015-11-26T05:22:24Z by Yeti Hunter

My edit had no effect on this overlap, it was there before my edit. .

See also
https://www.subiaco.wa.gov.au/Privacy-and-Disclaimer
that has
Copyright notice

The material produced by the City of Subiaco on this website is protected by copyright under the Copyright Act 1968.

Note ... ther is a copyright notice at the bottom of their first web page ... do you have permission to use their date?

Note 2 ... the suburban boundary is not closed... See https://tools.geofabrik.de/osmi/?view=areas&lon=115.80979&lat=-31.98572&zoom=12

Hi,
Welcome to OSM.

This changeset broke (removed a section) of the administration boundary for Majors Creek and Jembaicumbene. I have repaired these.
Administration boundaries are not something that moves often, they need little work. In NSW they are visible on the LPI Base Map for use in OSM. They are usually 'relationships' - groups of ways, each way is usually shared between 2 administration districts .. they are not easy for a beginner to deal with.

Don't let this discourage you. There is lots to map.

Please explain:

Source of boundary for 'Cobargo Apex Park'.

Source of name for 'Cobargo Apex Park' and why you deleted the name 'Cobargo Town Park' as seen on the LIP Base map.

Source of the name 'Sculpture Walkway'.

Source of the path 'Sculpture Walkway'.

Source for the barrier Way: 771340263 - particularly where hidden under the bridge and trees.

way/766791536 is not shown as a swap in either the LPI Base Map nor The LPI Topo map. Yet you have it tagged as a swamp.

relation/10693428 also is not shown as a wetland nor a swamp in the LPI Base Map nor The LPI Topo map. Yet you have it tagged as a wetland, previously you had it tagged as a swamp.
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The only swamp area shown on the LPI Base Map and the LPI Topo map is Way: 771395490.

No. The site has more than one hospital .. and none of the names are 'NSW Hospital'.

The building is not underground. The error is the overlap of one building with another.

Actually there are 2 buildings here - as can be seen by the boundary wall..

Fixed.