Explain the data values in earth_mask grids

[seisman]

https://www.generic-mapping-tools.org/remote-datasets/earth-masks.html

The documentation for earth-mask does not explain what the values mean in the earth-mask grids, although I can guess that 0 means ocean and 1 means land from the legend of the top figure.

I think we should:

• Clearly explain the meaning of the values 0-4
• Give the command that is used to generate the earth_mask grids (e.g., grdlandmask -N0/1/2/3/4)

[PaulWessel]

It certainly can be improved. We have information about levels in coast and gshhg modules but there we talk about the levels of the lines. Here we are talking about the areas between the levels (or in the case of the ocean, the areas outside level 1 (shoreline). So a better description might be

0. Ocean areas beyond the shoreline
1. Land areas inside the shoreline
2. Lakes inside the land area
3. Islands in lakes in the land area
4. Smaller lakes in islands that are found in lakes inside the land area

Not many of category 4 but there are at least one - not visible in this plot (neither are category 3 I think unless using full resolution).

I can work on this tomorrow unless you want to use this and put it in the right place. I think a link to the coast and/or gshhg documentation is probably also helpful here given the two Antarctica shorelines.

[PaulWessel]

Hi @seisman, looking at this information, isn't it pretty clear anyway?

[joa-quim]

I don't see why we are distributing masks that go beyond level 2 (actually I don't understand why we are even distributing mask grids at all that can be computed with a one-liner.)

[seisman]

Hi @seisman, looking at this information, isn't it pretty clear anyway?

Do you mean this sentence?

Given that GSHHG contains 5 levels (ocean, land, lake, island-in-lake, pond-in-island-in-lake) corresponding to levels 0-4, the mask grids were computed to reflect those 5 levels.

When I read this sentence, I know that there are 5 levels 0-4, but I'm still unsure if grid value=0 means level 0. So I feel a description you posted in #37 (comment) is better.

[PaulWessel]

I don't see why we are distributing masks that go beyond level 2 (actually I don't understand why we are even distributing mask grids at all that can be computed with a one-liner.)

Please try making a global GSHHG mask at full resolution and watch the clock...