Watering and draining the Earth (and other celestial objects)

What the Earth would look like if the sea level suddenly changed? And what would be the Moon, Mars and Venus if they had as much water as the Earth?

Check this on the following sets of maps and compare our Earth to other astronomical objects.

World maps. On this first set of maps, you can see how the world would be if the sea level decreased or increased from -100m to +100m by steps of 10m. Click to enlarge and browse maps.

1024×576  1280×720

Other world maps. On this second set of maps, the sea level goes from -1000m to +1000m by steps of 100m. Click to enlarge and browse maps.

1024×576  1280×720

Note that the maps are bedrock, i.e. without any ice surface. That’s why Antarctica forms several islands and a hole is on the center of Greenland.

The map associated with a fall of 100m of the sea level might represent the bedrock Earth 18000 years ago (ignoring the plate tectonic effects). On that map, you can observe that Russia and the USA merge together, as the United Kingdom with mainland Europe. For comparison, if all the ice melted on the Earth, the sea level would increase by 60m.

Celestial objects maps. On this final set of maps, let’s see the Moon, Venus and Mars with about 70% of their surface covered by water. Click to enlarge and browse maps.

1024×576  1280×720

The Moon is full of craters, and strangely the far side (on the center of the map) is higher than the near side (on the right and on the left).

Venus is a quite flat planet, except on Ishtar Terra (on the north) and on Aphrodite Terra (on the right on the map).

Finally, observe the remarkable Martian dichotomy and try to find:

Disclaimer: those maps have been designed for entertainment and this post does not pretend to be a scientific production.

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How to make those plots? I proceed in five steps.

  1. Get the data
  2. Transform it into raw files (with gdal)
  3. Files are big, reduce them (with the stream editors sed and awk)
  4. Plot data (with R)
  5. Make html (using a jQuery slider)

Get the data. I get topographic data of the Earth from the NOAA website (see this, this and this). I took the bedrock file version with xyz grid format and 10′ cell size. For the Moon, I find data from the NAOJ website (you have to create a free account before downloading). For Venus, you can pick the file here. Finally, for Mars, data are available on the MOLA subsite of the NASA (I took megt90n000cb img and lbl files). I haven’t found any data for Mercury (I would be grateful if someone could send it to me).

Transform it into text files. Some files are not in raw text files, i.e. some files cannot be open directly with a text editor. Those are Mars and Venus data files, which have respectively “.img” and “.grd” filename extensions. I convert them into xyz files, i.e. text files with on each line the longitude, the latitude and the height. Thanks to K.J. Bennett, I was able to do this with the gdal-bin package and the following line code.

gdal_translate -of XYZ megt90n000cb.lbl megt90n000cb.txt

Files are big, reduce them. On my personal computer, it is difficult to manage text files with a size greater than 100 MB. Here, the data files for Venus and the Moon are respectively 1.5 GB and 500 MB. To read them, I reduce them by taking only some lines. I take the Moon data file as an example. I work here under Linux, but the following can be adapted in other operating systems. To read the beginning of the file, I use the “head” command:

head -30000 lalt_topo_ver3.grd.txt >firstLines.txt

I observe that there are 5760 lines for each latitude, then using the “split” command,

split -d -l5760 -a4 lalt_topo_ver3.grd.txt

I find out that the data consider 5760×2880 lines.

Then, I delete every two lines with sed:

sed 'n;d' lalt_topo_ver3.grd.txt >moon1-0.txt

The new file has now 2880×2880 lines.

Next, to delete m lines every 2m with m=2880, I run this awk script (thanks to dubcek):

m=2880; awk -v m=$m '!((NR-1)%m) {n=!n} !n' moon1-0.txt >moon1-1.txt

I finally obtain a readable 2880×1440 lines file.

Plot data and make html. I use R and the functions “contour” and “filled.contour” to plot data. The R file is available here. Notice that for those plots, I take the Wikipedia conventions for topographic maps. Finally, I bring together the map pictures with a jQuery image slider called Coin Slider.

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5 thoughts on “Watering and draining the Earth (and other celestial objects)

  1. Hi ahstat, I’m impressed by your work and tried source topography-global.R, but got this error:
    [1] “1 on 30”
    Error in .Internal(filledcontour(as.double(x), as.double(y), z, as.double(levels), :
    there is no .Internal function ‘filledcontour’

    After I uncomment Line19, got this error:
    Error in plot.window(xlim = c(0, 1), ylim = range(levels), xaxs = “i”, :
    object ‘intervals’ not found

    I’m not familiar with R, please help solve this problem. Thanks.

  2. Hi hwhshq,
    thank you for your interest.
    “.Internal(filledcontour)” has been replaced by “.filled.contour” in the new versions of R.
    I updated the R file on this page, now it should works on R 3.x.

    Let me know if you plot some new cool maps!
    Alexis

  3. These maps are amazing – but have you considered doing a series of images with different sea levels for Mars and Venus, and you did for Earth? That would be fascinating!

  4. Pingback: If All The Ice Melted | Ritechoice Energy

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