Accurate way to add Ocean/Sea?

[David Sidwell]

Hi All,

Am doing take of my large (B0) wall map, for road trips.  Basically landscape, Melb up and over to ~Adelaide and ~ Canberra. Only showing 'places (Cities ...to... Hamlets) ' and 'roads', that's it.

I'm happy with all the basic layers and rule-driven labels, but I can't get the sea/ocean to fill the white (non-land) bits (ie. south in this screen shot). AI suggested a few things, but all resulted in 'aqua over everything' in the Map or Layout.

ne_10m_ocean.shp gets me most of the way, but clearly doesn't align with my other layers (see below). Any smart ways to do this? Or other more accurate ocean data sources?

Ta.

[Luke Kirkwood]

It’s a bit of cheats way, but you could always set the background colour in QGIS options, as long as you don’t have transparency on the land layers

Here I have a land layer and no water layer, just the blank background shaded blue

You could also duplicate your land layer and render it as Inverted Polygons. That way it is a 1:1 inversion and then you can keep transparencies. Just means more computing power required. 

On 25 Sep 2025, at 5:17 pm, David Sidwell <sidwel...@gmail.com> wrote:

Hi All,

Am doing take of my large (B0) wall map, for road trips.  Basically landscape, Melb up and over to ~Adelaide and ~ Canberra. Only showing 'places (Cities ...to... Hamlets) ' and 'roads', that's it.

I'm happy with all the basic layers and rule-driven labels, but I can't get the sea/ocean to fill the white (non-land) bits (ie. south in this screen shot). AI suggested a few things, but all resulted in 'aqua over everything' in the Map or Layout.

ne_10m_ocean.shp gets me most of the way, but clearly doesn't align with my other layers (see below). Any smart ways to do this? Or other more accurate ocean data sources?

Ta.

<ss.20250925_170914_Wall_map_-_Sept_2025_Natural_Earth_2025_and_geofab.png>

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[David Sidwell]

Thanks, Luke. Big step forward, thanks to your clue. I found that my land layer had its Rendering Opacity at ~30% as part of an earlier test to get its colour changed.  Back to 100% and QGIS masked the land out from the map's BG, so only the 'non-land' went aqua.  Now to get it to xfer to the Layout, but I'll work that out...hopefully.

I had probably missed that as its (default) name has 'Aus-coastline' in it, so I didn't associate that with the land mass per se. Still learning.  

David Sidwell 

 Senior Technical Writer (semi-retired)
   Newport, Victoria, Australia  
   M: 0438 397 822   

      https://www.davidphoto.org/    (still migrating, should be ok)

      Sometimes blogging about Music, Science, Movies, Hiking, History, Technology, TV...

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